Thesis (M.S.)--University of North Carolina at Wilmington, 2005. / Includes bibliographical references (leaves: 62-66)

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Includes bibliographical references.

Thesis (M.S.)--University of North Carolina at Wilmington, 2005. / Includes bibliographical references (leaves: 66-75)

Thesis (Ph. D.)--University of Rhode Island, 2003. / Typescript. Includes bibliographical references (v. 2, leaves 331-354).

Winter flounder, Pleuronectes americanus, is being developed for aquaculture in Atlantic Canada. Since larval culture has been successful, research can now address problems at the juvenile stage such as weaning, diet and optimal growth environment. Weaning, a critical stage in culture of any flatfish species, is the switch from live food to an artificial diet. In a three month study, I was able to wean wild young-of-the year winter flounder from live, cultured Artemia onto dry food. Specific growth rates and food conversion indicated the artificial diet was a better food source than Artemia. In a second study, I was able to wean recently-metamorphosed winter flounder reared in the laboratory, onto two artificial diets which differed in price and lipid content. There was no difference between the inexpensive salmonid starter diet and the more costly Nippai diet on growth and survival. In a third study, I examined the effects of temperature and density on wild year 0 and 1 winter flounder reared on dry salmonid diet. There was no effect of density on growth and survival over the ranges tested. Greatest growth occurred at 15$ sp circ$C, although survival was highest at ambient temperature.

Collagenases were extracted from the skeletal muscle of winter flounder (Pseudopleuronectes americanus) with Tris-HCl buffer, pH 7.4, containing 5 mM CaCl$ sb2.$ The crude extract in the active form was purified by ammonium sulfate fractionation, followed by a succession of column chromatographic steps which included ion-exchange, immobilized metal affinity and size-exclusion in the Fast Protein Liquid Chromatography (FPLC) system. The trypsin-like and chymotrypsin-like activities of the crude extract diminished with purification. A comparative study of the collagenase fraction from ion-exchange chromatography (IEX-1) and the commercial collagenase fraction from Clostridium histolyticum indicated that the two enzymes were similar with respect to their response to temperature but differed with respect to their response to pH. The enzymes differed slightly in terms of their thermal and pH stabilities. The winter flounder collagenase fraction from size-exclusion chromatography (SEC) had a higher optimum pH temperature than the IEX-1 fraction as well as the commercial collagenase. However, both SEC and the IEX-1 extracts had the same optimum pH. The collagenase fraction from SEC had a slightly lower thermal stability than the IEX-1 fraction and the commercial collagenase. / The higher catalytic efficiency (V$ sb{ rm max}$/K$ sb{ rm m}$') and the lower $ Delta$G values for C. histolyticum collagenases showed that bacterial collagenases are better catalysts than winter flounder skeletal muscle collagenases for the PZ-peptide hydrolase reaction at 37$ sp circ$C and pH 7.1. / Zymography revealed the presence of two collagenase isoenzymes from the fish muscle, designated as WFC-1 and WFC-2 with molecular weights of 79,600 and 75,500, respectively. WFC-1 was separated from WFC-2 by electrophoretic blotting onto the PVDF membrane. The amino acid composition of WFC-1 and WFC-2 were closely related. / The fish collagenases were inhibited by metal chelators, EDTA and 1,10-phenanthroline suggesting that these enzymes are metalloproteases. The enzyme activity in the presence of EDTA and 1,10-phenanthroline were recovered upon addition of low levels of calcium and zinc ions, respectively. Higher levels of these metal ions inhibited the isoenzymes. 2-Mercaptoethanol and dithiothreitol were also effective inhibitors.

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Structure-function relationships for an alanine-rich, α-helical antifreeze polypeptide (AFP) from winter flounder were studied with the goal of understanding how AFPs depress the freezing point of water. A 37-residue native AFP and 23 analogs with systematic variations in the polypeptide chain were synthesized, and the α-helix content, antifreeze activity, and effect on growth rates of ice crystals along the a and c axes were determined. The results indicate that both the regularly spaced threonine and asparagine (or aspartic acid) residues are critical for maximal activity, and that the asymmetric arrangement of these residues on the helix face causes asymmetric adsorption of AFPs on the ice surface. Charged-residues, except for C-terminal Arg, are not very critical for antifreeze activity. Studies of hydrophobic residue mutants showed that the overall hydrophobicity is not particularly important. However, the Ala residue in position 17 appears to be important, because replacement with a bulky group abolishes antifreeze activity, presumably by interfering with the favorable side-to-side hydrophobic A model for binding of the winter flounder AFP to ice is proposed, whereby the AFP inhibits the growth of ice crystals by hydrogen bonding of Thr, Asn and Asp side chains in a specific pattern to the { 20 21 } hexagonal bipyramidal planes of ice, unidirectionally along the vector <1102>. It is further proposed that ice crystal growth inhibition occurs by a two-step mechanism: first individual AFP molecules hydrogen bond to ice reversibly, allowing slow growth of ice crystal; then at sufficiently high AFP concentrations, the AFP molecules begin to pack together on the binding surface by cooperative, side-to-side, hydrophobic interpeptide interactions, resulting in essentially irreversible binding and arrested ice crystal growth. The D-enantiomer of the AFP was also synthesized. The D and L-enantiomers alone, as well as a 50:50 mixture of D and L, all show identical antifreeze activity. These results indicate that complete coverage of the ice surface is not necessary, and suggest a model whereby AFP molecules bind in patches on the ice surface. / 2031-01-01

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Thesis (Ph.D.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 196-217.