Glucose 1,6-bisphosphate is an important small molecule involved in the regulation of glycolysis. Four enzymes synthesize this compound. One enzyme is known to degrade it, glucose 1,6-bisphosphatase. Other groups have produced work that indicates that there are two isoforms of this enzyme, one predominant in the brain and one in the muscle. This thesis contains the work performed in attempts to isolate and characterize the muscle isoform of glucose 1,6-bisphosphatase. While this enzyme was not isolated, much was learned about it and the results from this work may help in the future identification of this enzyme.

The glpX gene of Escherichia coli encodes fructose 1,6-bisphosphatase II (FBPase II), an enzyme that would appear to be redundant with FBPase I, encoded by fbp. However, glpX mutants have no apparent phenotype, while fbp mutants are unable to grow on gluconeogenic substrates as sole carbon sources, suggesting that GlpX function is insufficient for growth of fbp mutants under these conditions. To gain insight into the physiological functions of the FBPases, regulation of glpX expression was investigated. It was found that glpX is transcribed as part of a complex glpFKX operon containing promoters upstream of glpF, glpK and glpX (PglpF, PglpK, PglpX, respectively). Transcription start sites of PglpX were found at -24 and -41 relative to the ATG translation initiation site using primer extension analysis. Unlike PglpF, these newly found promoters were not subject to regulation by GlpR or cAMP-CRP. Cra (Catabolite Repressor/Activator) positively regulated expression from PglpK and PglpX by increasing transcription approximately 2 fold. Western analysis using GlpX polyclonal antibodies revealed that GlpX levels were higher in cultures grown on glycerol compared with levels in maltose- or glucose-grown cultures (glycerol>maltose>glucose). Various strains and growth conditions were used to show that GlpX levels are regulated by GlpR, suggesting that PglpF can give rise to expression of glpX. GlpX protein was present in a strain containing a polar insertion in glpK, indicating that PglpX can also give rise to expression of glpX. Strains deficient in FBPase I or CsrA (carbon starvation regulator) did not reveal any difference in GlpX levels with respect to the wild type. All of these data indicate that glpX expression is achieved by its own promoter as well as the operon promoter, PglpF. Finally, the results show that the delta-fbp phenotype is not due to the absence of GlpX. / Ph. D.

In Escherichia coli, the utilization of glycerol and sn-glycerol 3-phosphate is mediated by gene products of the glp regulon. The regulon encompasses five operons, including the glpFKX operon. Although glpF and glpK encode glycerol diffusion facilitator and glycerol kinase,respectively, the function of glpX was unknown. In the present work, we show that glpX encodes a fructose 1,6-bisphosphatase (FBPase), which catalyzes the hydrolysis of fructose 1,6-bisphosphate to fructose 6-phosphate and phosphate. The purified FBPase was dimeric, dependent on Mn2+ for activity and exhibited an apparent Km of 35 μM for fructose 1,6-bisphosphate. The enzyme was inhibited by ADP, ATP and phosphate and activated by PEP. The attributes of the glpX-encoded FBPase were different from those of the previously characterized E. coli FBPase encoded by fbp. Mutants deleted in fbp (Δfbp) display a growthnegative phenotype on gluconeogenic carbon sources such as glycerol, indicating the inability of chromosomal glpX+ to complement Δfbp. However, a Δfbp mutation was complemented by overexpression of glpX+. In contrast, a glpX mutant exhibited a growth-positive phenotype on glycerol, glucose or fructose media. Surprisingly, a double mutant strain glpX pfkA (6-phosphofructokinase I) was more inhibited in growth on glucose and glycerol media than the pfkA parent. Carbohydrate metabolism in the pfkA background may be affected by the glpXmediated change in fructose 6-phosphate/fructose 1,6-bisphosphate levels. FBPase activities of soluble proteins separated by non-denaturing PAGE were visualized, showing a novel (third) FBPase, perhaps encoded by the glpX homolog, yggF. / Master of Science

<p>Methylglyoxal (MG) is a reactive glucose metabolite and a known causative factor for hypertension and diabetes. Hydrogen sulfide (H₂S), on the other hand, is a gasotransmitter with multifaceted physiological functions, including anti-oxidant and vasodilatory properties. The present study demonstrates that MG and H₂S can interact with and modulate each other's functions. Upon <i>in vitro</i> incubations, we found that MG and H₂S can directly interact to form three possible MG-H₂S adducts. Furthermore, the endogenous production level of MG or H₂S was significantly reduced in a concentration-dependent manner in rat vascular smooth muscle cells (A-10 cells) treated with NaHS, a H₂S donor, or MG, respectively. Indeed, MG-treated A-10 cells exhibited a concentration-dependent down-regulation of the protein and activity level of cystathionine &gamma;-lyase (CSE), the main H₂S-generating enzyme in the vasculature. Moreover, H₂S can induce the inhibition of MG-generated ROS production in a concentration-dependent manner in A-10 cells. In 6-22 week-old CSE knockout male mice (CSE^-/-), mice with lower levels of vascular H₂S, we observed a significant elevation in MG levels in both plasma and renal extracts. Renal triosephosphates were also significantly increased in the 6-22 week-old CSE^-/- mice. To identify the source of the elevated renal MG levels, we found that the activity of fructose-1,6-bisphosphatase (FBPase), the rate-limiting enzyme in gluconeogenesis, was significantly down-regulated, along with lower levels of its product (fructose-6-phosphate) and higher levels of its substrate (fructose-1,6-bisphosphate) in the kidney of 6-22 week-old CSE^-/- mice. We have also observed lower levels of the gluconeogenic regulator, peroxisome proliferator-activated receptor-&gamma; coactivator (PGC)-1&alpha;, and its down-stream targets, FBPase-1 and -2, phosphoenolpyruvate carboxykinase (PEPCK), and estrogen-related receptor (ERR)&alpha; mRNA expression levels in renal extracts from 6-22 week-old CSE^-/- mice. Likewise, FBPase-1 and -2 mRNA levels were also significantly down-regulated in aorta tissues from 14-16 week-old CSE^-/- mice. Administration of 30 and 50 &#x00B5;M NaHS induced a significant increase in FBPase-1 and PGC-1&alpha; in rat A-10 cells. We have also observed a significant up-regulation of PEPCK and ERR&alpha; mRNA expression levels in 50 &#x00B5;M NaHS-treated A-10 cells, further confirming the involvement of H₂S in regulating the rate of gluconeogenesis and MG formation. Overall, this unique study demonstrates the existence of a negative correlation between MG and H₂S in the vasculature. Further elucidation of this cross-talk phenomenon between MG and H₂S could lead to more elaborate and effective therapeutic regimens to combat metabolic syndrome and its related health complications.</p>

<p>Methylglyoxal (MG) is a reactive glucose metabolite and a known causative factor for hypertension and diabetes. Hydrogen sulfide (H₂S), on the other hand, is a gasotransmitter with multifaceted physiological functions, including anti-oxidant and vasodilatory properties. The present study demonstrates that MG and H₂S can interact with and modulate each other's functions. Upon <i>in vitro</i> incubations, we found that MG and H₂S can directly interact to form three possible MG-H₂S adducts. Furthermore, the endogenous production level of MG or H₂S was significantly reduced in a concentration-dependent manner in rat vascular smooth muscle cells (A-10 cells) treated with NaHS, a H₂S donor, or MG, respectively. Indeed, MG-treated A-10 cells exhibited a concentration-dependent down-regulation of the protein and activity level of cystathionine &gamma;-lyase (CSE), the main H₂S-generating enzyme in the vasculature. Moreover, H₂S can induce the inhibition of MG-generated ROS production in a concentration-dependent manner in A-10 cells. In 6-22 week-old CSE knockout male mice (CSE^-/-), mice with lower levels of vascular H₂S, we observed a significant elevation in MG levels in both plasma and renal extracts. Renal triosephosphates were also significantly increased in the 6-22 week-old CSE^-/- mice. To identify the source of the elevated renal MG levels, we found that the activity of fructose-1,6-bisphosphatase (FBPase), the rate-limiting enzyme in gluconeogenesis, was significantly down-regulated, along with lower levels of its product (fructose-6-phosphate) and higher levels of its substrate (fructose-1,6-bisphosphate) in the kidney of 6-22 week-old CSE^-/- mice. We have also observed lower levels of the gluconeogenic regulator, peroxisome proliferator-activated receptor-&gamma; coactivator (PGC)-1&alpha;, and its down-stream targets, FBPase-1 and -2, phosphoenolpyruvate carboxykinase (PEPCK), and estrogen-related receptor (ERR)&alpha; mRNA expression levels in renal extracts from 6-22 week-old CSE^-/- mice. Likewise, FBPase-1 and -2 mRNA levels were also significantly down-regulated in aorta tissues from 14-16 week-old CSE^-/- mice. Administration of 30 and 50 &#x00B5;M NaHS induced a significant increase in FBPase-1 and PGC-1&alpha; in rat A-10 cells. We have also observed a significant up-regulation of PEPCK and ERR&alpha; mRNA expression levels in 50 &#x00B5;M NaHS-treated A-10 cells, further confirming the involvement of H₂S in regulating the rate of gluconeogenesis and MG formation. Overall, this unique study demonstrates the existence of a negative correlation between MG and H₂S in the vasculature. Further elucidation of this cross-talk phenomenon between MG and H₂S could lead to more elaborate and effective therapeutic regimens to combat metabolic syndrome and its related health complications.</p>