<p>Amino-acid radical enzymes have been studied extensively for 30 years but the experimental barriers to determine the thermodynamic properties of their key radical cofactors are so challenging that only a handful of reports exist in the literature. This is a major drawback when trying to understand the long-range radical transfer and/or catalytic mechanisms of this important family of enzymes. Here this issue is addressed by developing a library of well-structured model proteins specifically designed to study tyrosine and tryptophan radicals. The library is based on a 67-residue three-helix bundle (α₃W) and a 117-residue four-helix bundle (α₄W). α₃W and α₄W are single-chain and uniquely structured proteins. They are redox inert except for a single radical site (position 32 in α₃W and 106 in α₄W). Papers I and II describe the design process and the protein characteristics of α₄W as well as a voltammetry study of its unique tryptophan. Paper III and V describe two projects based on α₃C, which is a Trp-32 to Cys-32 variant of α₃W. In Paper III we use α₃C to investigate what effect the degree of solvent exposure of the phenolic OH group has on the redox characteristics of tyrosine analogs. We show that the potential of the PhO•/PhOH redox pair is dominated by interactions with the OH group and that the environment around the hydrophobic part of the phenol has no significant impact. In addition, we observe that interactions between the phenolic OH group and the protein matrix can raise the phenol potential by 0.11-0.12 V relative to solution values. The α₃C system is extended in Paper V to study quinone redox chemistry. Papers III and V contain protocols to generate the cofactor-containing α₃C systems and descriptions of their protein properties. Paper IV describes efforts to redesign α₃Y (a Trp-32 to Tyr-32 variant of α₃W) to contain an interacting Tyr-32/histidine pair. The aim is to engineer and study the effects of a redox-induced proton acceptor in the Tyr-32 site.</p>

Amino-acid radical enzymes have been studied extensively for 30 years but the experimental barriers to determine the thermodynamic properties of their key radical cofactors are so challenging that only a handful of reports exist in the literature. This is a major drawback when trying to understand the long-range radical transfer and/or catalytic mechanisms of this important family of enzymes. Here this issue is addressed by developing a library of well-structured model proteins specifically designed to study tyrosine and tryptophan radicals. The library is based on a 67-residue three-helix bundle (α3W) and a 117-residue four-helix bundle (α4W). α3W and α4W are single-chain and uniquely structured proteins. They are redox inert except for a single radical site (position 32 in α3W and 106 in α4W). Papers I and II describe the design process and the protein characteristics of α4W as well as a voltammetry study of its unique tryptophan. Paper III and V describe two projects based on α3C, which is a Trp-32 to Cys-32 variant of α3W. In Paper III we use α3C to investigate what effect the degree of solvent exposure of the phenolic OH group has on the redox characteristics of tyrosine analogs. We show that the potential of the PhO•/PhOH redox pair is dominated by interactions with the OH group and that the environment around the hydrophobic part of the phenol has no significant impact. In addition, we observe that interactions between the phenolic OH group and the protein matrix can raise the phenol potential by 0.11-0.12 V relative to solution values. The α3C system is extended in Paper V to study quinone redox chemistry. Papers III and V contain protocols to generate the cofactor-containing α3C systems and descriptions of their protein properties. Paper IV describes efforts to redesign α3Y (a Trp-32 to Tyr-32 variant of α3W) to contain an interacting Tyr-32/histidine pair. The aim is to engineer and study the effects of a redox-induced proton acceptor in the Tyr-32 site.

In order to investigate the structural features responsible for the cytotoxicity of the naturally occurring lignan nordihydroguaiaretic acid, the synthesis of four structural analogues of NDGA is proposed for the purpose of studying their oxidative metabolism. One analogue in particular (1), a mono-catechol analogue, is successfully synthesized employing a double Stobbe condensation approach. Following synthesis of this compound a series of oxidation experiments is performed consisting of: incubation in rat liver microsomes with and without the trapping agent glutathione (GSH), oxidation with mushroom tyrosinase, oxidation with silver oxide, and oxidation with horseradish peroxidase. Results are analyzed via HPLC and UPLC-MS. It is found that 1 does not autoxidize at pH 7.4 as NDGA does. Two products are produced during incubation of 1 in rat liver microsomes with UPLC-ESI(-)-MS results giving m/z of 879.2 and 574.18. This is consistent with 1 plus 2 GSH and 1 plus 1 GSH respectively; confirming 1 will oxidize to an electrophilic moiety. Oxidation with mushroom tyrosinase is found to produce high levels of product two with m/z 574.2. Oxidation with horseradish peroxidase is found to produce high levels of the m/z 879.2 product. Silver Oxide produced multiple products rather than the expected one major product, but most are found to be inconsistent with the products seen during rat liver microsomal incubation, and are not pursued.

The development of reversible and irreversible inhibitors of steroid sulfatase (STS) and protein tyrosine phosphatase 1B (PTP1B) is reported herein. STS belongs to to the aryl sulfatase family of enzymes that have roles in diverse processes such as hormone regulation, cellular degradation, bone and cartilage development, intracellular communication, and signalling pathways. STS catalyzes the desulfation of sulfated steroids which are the storage forms of many steroids such as the female hormone estrone. Its crucial role in the regulation of estrogen levels has made it a therapeutic target for the treatment of estrogen-dependent cancers. Estrone sulfate derivatives bearing 2- and 4-mono- and difluoromethyl substitutions were examined as quinone methide-generating suicide inhibitors of STS with the goal of developing these small molecules as activity-based probes for proteomic profiling of sulfatases. Kinetic studies suggest that inhibition by the monofluoro derivatives is a result of a quinone methide intermediate that reacts with active-site nucleophiles. However, the main inhibition pathway of the 4-difluoromethyl derivative involved an unexpected process in which initially formed quinone methide diffuses from the active site and decomposes to an aldehyde in solution which then acts as a potent, almost irreversible STS inhibitor. This is the first example where this class of inactivator functions by in situ generation of an aldehyde. 6- and 8-mono- and difluoromethyl coumarin derivatives were also examined as quinone methide-generating suicide inhibitors of STS. The 6-monofluoromethyl derivative acted as a classic suicide inhibitor. The partition ratio of this compound was found to be very large indicating that this class of compounds is not likely suitable as an activity-based probe for proteomic profiling of sulfatases. Boronic acids derived from steroid and coumarin platforms were also examined as STS inhibitors with the goal of improving our understanding of substrate binding specificity of STS. Inhibition constants in the high nanomolar to low micromolar range were observed for the steroidal derivatives. The coumarin derivatives were poor inhibitors. These results suggest that the boronic acid moiety must be attached to a platform very closely resembling a natural substrate in order for it to impart a beneficial effect on binding affinity compared to its phenolic analog. The mode of inhibition observed was reversible and kinetic properties corresponding to the mechanism for slow-binding inhibitors were not observed. PTP1B catalyzes the dephosphorylation of phosphotyrosine residues in the insulin receptor kinase and is a key enzyme in the down regulation of insulin signaling. Inhibitors of PTP1B are considered to have potential as therapeutics for treating type II diabetes mellitus. The difluoromethylenesulfonic (DFMS) acid group, one of the best monoanionic phosphotyrosine mimics reported in the literature, was examined as a phosphotyrosine (pTyr) mimic in a non-peptidyl platform for PTP1B inhibition. The DFMS-bearing inhibitor was found to be an approximately 1000-fold poorer inhibitor than its phosphorus analogue. It was also found that the fluorines in the DFMS inhibitor contributed little to inhibitory potency. In addition, [sulfonamido(difluoromethyl)]-phenylalanine (F2Smp) was examined as a neutral pTyr mimic in commonly used hexapeptide and tripeptide platforms. F2Smp was found to be a poor pTyr mimic. These inhibition studies also revealed that the tripeptide platform is not suitable for assessing pTyr mimics for PTP1B inhibition. Taken together, the kinetic data on the inhibition of STS and PTP1B provide valuable information relevant for future design of inhibitors of these two therapeutic targets.

The development of reversible and irreversible inhibitors of steroid sulfatase (STS) and protein tyrosine phosphatase 1B (PTP1B) is reported herein. STS belongs to to the aryl sulfatase family of enzymes that have roles in diverse processes such as hormone regulation, cellular degradation, bone and cartilage development, intracellular communication, and signalling pathways. STS catalyzes the desulfation of sulfated steroids which are the storage forms of many steroids such as the female hormone estrone. Its crucial role in the regulation of estrogen levels has made it a therapeutic target for the treatment of estrogen-dependent cancers. Estrone sulfate derivatives bearing 2- and 4-mono- and difluoromethyl substitutions were examined as quinone methide-generating suicide inhibitors of STS with the goal of developing these small molecules as activity-based probes for proteomic profiling of sulfatases. Kinetic studies suggest that inhibition by the monofluoro derivatives is a result of a quinone methide intermediate that reacts with active-site nucleophiles. However, the main inhibition pathway of the 4-difluoromethyl derivative involved an unexpected process in which initially formed quinone methide diffuses from the active site and decomposes to an aldehyde in solution which then acts as a potent, almost irreversible STS inhibitor. This is the first example where this class of inactivator functions by in situ generation of an aldehyde. 6- and 8-mono- and difluoromethyl coumarin derivatives were also examined as quinone methide-generating suicide inhibitors of STS. The 6-monofluoromethyl derivative acted as a classic suicide inhibitor. The partition ratio of this compound was found to be very large indicating that this class of compounds is not likely suitable as an activity-based probe for proteomic profiling of sulfatases. Boronic acids derived from steroid and coumarin platforms were also examined as STS inhibitors with the goal of improving our understanding of substrate binding specificity of STS. Inhibition constants in the high nanomolar to low micromolar range were observed for the steroidal derivatives. The coumarin derivatives were poor inhibitors. These results suggest that the boronic acid moiety must be attached to a platform very closely resembling a natural substrate in order for it to impart a beneficial effect on binding affinity compared to its phenolic analog. The mode of inhibition observed was reversible and kinetic properties corresponding to the mechanism for slow-binding inhibitors were not observed. PTP1B catalyzes the dephosphorylation of phosphotyrosine residues in the insulin receptor kinase and is a key enzyme in the down regulation of insulin signaling. Inhibitors of PTP1B are considered to have potential as therapeutics for treating type II diabetes mellitus. The difluoromethylenesulfonic (DFMS) acid group, one of the best monoanionic phosphotyrosine mimics reported in the literature, was examined as a phosphotyrosine (pTyr) mimic in a non-peptidyl platform for PTP1B inhibition. The DFMS-bearing inhibitor was found to be an approximately 1000-fold poorer inhibitor than its phosphorus analogue. It was also found that the fluorines in the DFMS inhibitor contributed little to inhibitory potency. In addition, [sulfonamido(difluoromethyl)]-phenylalanine (F2Smp) was examined as a neutral pTyr mimic in commonly used hexapeptide and tripeptide platforms. F2Smp was found to be a poor pTyr mimic. These inhibition studies also revealed that the tripeptide platform is not suitable for assessing pTyr mimics for PTP1B inhibition. Taken together, the kinetic data on the inhibition of STS and PTP1B provide valuable information relevant for future design of inhibitors of these two therapeutic targets.

In order to investigate the structural features responsible for the cytotoxicity of the naturally occurring lignan nordihydroguaiaretic acid, the synthesis of four structural analogues of NDGA is proposed for the purpose of studying their oxidative metabolism. One analogue in particular (1), a mono-catechol analogue, is successfully synthesized employing a double Stobbe condensation approach. Following synthesis of this compound a series of oxidation experiments is performed consisting of: incubation in rat liver microsomes with and without the trapping agent glutathione (GSH), oxidation with mushroom tyrosinase, oxidation with silver oxide, and oxidation with horseradish peroxidase. Results are analyzed via HPLC and UPLC-MS. It is found that 1 does not autoxidize at pH 7.4 as NDGA does. Two products are produced during incubation of 1 in rat liver microsomes with UPLC-ESI(-)-MS results giving m/z of 879.2 and 574.18. This is consistent with 1 plus 2 GSH and 1 plus 1 GSH respectively; confirming 1 will oxidize to an electrophilic moiety. Oxidation with mushroom tyrosinase is found to produce high levels of product two with m/z 574.2. Oxidation with horseradish peroxidase is found to produce high levels of the m/z 879.2 product. Silver Oxide produced multiple products rather than the expected one major product, but most are found to be inconsistent with the products seen during rat liver microsomal incubation, and are not pursued.

No description available.

A series of 1,2,3-dithiazolyl radicals have been prepared as spin-bearing radical ligands for coordination to paramagnetic transition metal and lanthanide ions to afford both interesting magnetic and potential conductive properties. The novel syntheses and full characterization of the ligands are described with the electronic properties investigated by both solution & solid-state EPR and cyclic voltammetry. The ligand structures are characterized by X-ray crystallography and the magnetic properties investigated. The ligands described herein represent the first reported 1,2,3-dithiazolyl radical ligands to coordinate to paramagnetic transition metal or lanthanide ion(s). The 1,2,3-dithiazoyl ligands described have been used to prepare a number of metal complexes and the structures have been fully characterized by X-ray crystallography. A diverse range of complexes including monomers, trimers and polymers have been synthesized and characterized. The solid-state and solution magnetic properties of the metal complexes have been investigated using a range of appropriate instrumental techniques, and are reported. The chelating properties of the 1,2,3-dithiazolyl ligands described are via an unprecedented motif. A para-naphthoquinone backbone is utilized with the fused 1,2,3dithiazolyl heterocyclic ring. The coordination geometry between the nitrogen atom and the quinone oxygen(s) allows for the variety of complexes reported, including the design objective of a polymeric paramagnetic coordination complex. A series of 1,2,5-thiadiazolyl radical anions have been prepared as spin-bearing radical ligands for the coordination to paramagnetic transition metal and lanthanide ions to enable both interesting magnetic and conductive properties. The syntheses and full characterizations are described with the electronic properties investigated by solution EPR and cyclic voltammetry. The ligand structures are characterized by X-ray crystallography and both the magnetic properties and conductivity (including Extended Hückel Theory calculations) are investigated and reported. A series of novel fluorinated 1,2,5-thiadiazole closed shell neutral ligands have been prepared and characterized. The radical anion is studied in situ by EPR. All materials generated in the synthesis were sent to the National Cancer Institute (USA) for collaboration involving clinical cancer inhibition studies and the results are reported.

Darbo tikslas buvo ištirti nuo pirolo chinolinchinono (PQQ) priklausomų oksidoreduktazių veikimą homogeninėje ir heterogeninėje aplinkose ir jų pagrindu sukurti naujas bioelektrokatalizines sistemas. Tuo tikslu buvo kurtos impedimetrinės ir bioamperometrinės sistemos su nuo PQQ priklausomomis alkoholio (tADH ir mADH), gliukozės (GDH) ir fruktozės (FDH)dehidrogenazėmis naujų elektrodinių medžiagų pagrindu, parenkant optimalų fermento imobilizavimo būdą ir elektronų pernašos (EP) mediatorius. Fermentai ir sistemos tirtos klasikinės elektrochemijos, impedanso spektroskopijos, spektrofotometrijos, atominės jėgos mikroskopijos metodais. Nustatytos tADH ir mADH pKa reikšmės ir EP keliai, pagrindinės bioelektrocheminių sistemų charakteristikos, įvertinta heterogeninės aplinkos įtaka fermentų specifiškumui. Sukurtas imobilizavimo būdas leidžiantis išlaikyti GDH aktyvumą iki 9-ių mėnesių. Pirmą kartą parodyta, jog fermentai gali tiesiogiai re-oksiduotis ant poli - N - (N, N‘- dietil ditiokarbamoil etil amidoetil) – anilino ir grafito produktų. Nustatyta, jog 2-(3-nitro(fenil)amino)- cikloheksa-2,5-dien-1,4-dionas iki 10 kartų pagreitina FDH katalizuojamą fruktozės oksidaciją. Pirmą kartą parodyta, kad bioamperometrinės sistemos su FDH gali oksiduoti D(-)tagatozę. Tyrimų rezultatai pritaikyti kuriant alkoholių, angliavandenių ir anglies monoksido stebėjimo sistemas. / The aim of this work was to study the action of pyrroloquinoline quinone (PQQ) dependent oxidoreductases in homogeneous and heterogeneous ambiences and to create new bioelectrocatalytic systems based on these enzymes. Bioelectrochemical systems with PQQ dependent alcohol (sADH and mADH), glucose (GDH) and fructose (FDH) dehydrogenases were constructed by using new electrode materials, enzyme immobilization techniques and electron transfer (ET) mediators. Enzymes and systems were studied by different electrochemical methods and atomic force microscopy. pKa values and ET pathways in bioelectrochemical systems were determined for sADH and mADH. The main characteristics of systems and influence of heterogeneous ambience to the specificity of the enzymes were determined. The GDH immobilization method, which ensures enzyme activity up to 9 months, was created. The direct ET from reduced enzymes active sites to poly(N-(N’,N’-diethyldithiocarbamoylethylamidoethyl)aniline) and graphite oxidation products was revealed for the first time. It was observed that 2-(3-nitro(phenyl)amino)- ciclohexa-2,5-dien-1,4-dione is the most effective mediator for FDH. The ability of bioamperometric systems with FDH to oxidize D(-)tagatose was determined for the first time. It was shown, that bioamperometric systems based on PQQ dependent enzymes can be applied for detection of alcohols, carbohydrates and carbon monoxide.

Darbo tikslas buvo ištirti nuo pirolo chinolinchinono (PQQ) priklausomų oksidoreduktazių veikimą homogeninėje ir heterogeninėje aplinkose ir jų pagrindu sukurti naujas bioelektrokatalizines sistemas. Tuo tikslu buvo kurtos impedimetrinės ir bioamperometrinės sistemos su nuo PQQ priklausomomis alkoholio (tADH ir mADH), gliukozės (GDH) ir fruktozės (FDH)dehidrogenazėmis naujų elektrodinių medžiagų pagrindu, parenkant optimalų fermento imobilizavimo būdą ir elektronų pernašos (EP) mediatorius. Fermentai ir sistemos tirtos klasikinės elektrochemijos, impedanso spektroskopijos, spektrofotometrijos, atominės jėgos mikroskopijos metodais. Nustatytos tADH ir mADH pKa reikšmės ir EP keliai, pagrindinės bioelektrocheminių sistemų charakteristikos, įvertinta heterogeninės aplinkos įtaka fermentų specifiškumui. Sukurtas imobilizavimo būdas leidžiantis išlaikyti GDH aktyvumą iki 9-ių mėnesių. Pirmą kartą parodyta, jog fermentai gali tiesiogiai re-oksiduotis ant poli - N - (N, N‘- dietil ditiokarbamoil etil amidoetil) – anilino ir grafito produktų. Nustatyta, jog 2-(3-nitro(fenil)amino)- cikloheksa-2,5-dien-1,4-dionas iki 10 kartų pagreitina FDH katalizuojamą fruktozės oksidaciją. Pirmą kartą parodyta, kad bioamperometrinės sistemos su FDH gali oksiduoti D(-)tagatozę. Tyrimų rezultatai pritaikyti kuriant alkoholių, angliavandenių ir anglies monoksido stebėjimo sistemas. / The aim of this work was to study the action of pyrroloquinoline quinone (PQQ) dependent oxidoreductases in homogeneous and heterogeneous ambiences and to create new bioelectrocatalytic systems based on these enzymes. Bioelectrochemical systems with PQQ dependent alcohol (sADH and mADH), glucose (GDH) and fructose (FDH) dehydrogenases were constructed by using new electrode materials, enzyme immobilization techniques and electron transfer (ET) mediators. Enzymes and systems were studied by different electrochemical methods and atomic force microscopy. pKa values and ET pathways in bioelectrochemical systems were determined for sADH and mADH. The main characteristics of systems and influence of heterogeneous ambience to the specificity of the enzymes were determined. The GDH immobilization method, which ensures enzyme activity up to 9 months, was created. The direct ET from reduced enzymes active sites to poly(N-(N’,N’-diethyldithiocarbamoylethylamidoethyl)aniline) and graphite oxidation products was revealed for the first time. It was observed that 2-(3-nitro(phenyl)amino)- ciclohexa-2,5-dien-1,4-dione is the most effective mediator for FDH. The ability of bioamperometric systems with FDH to oxidize D(-)tagatose was determined for the first time. It was shown, that bioamperometric systems based on PQQ dependent enzymes can be applied for detection of alcohols, carbohydrates and carbon monoxide.