摘要:

ABSTRACTBuffalo milk proteins were covalently enriched with methionine (Met) during the enzymatic peptide modification (EPM) process. The maximal Met‐enrichment occurred when the α‐chymotryptic hydrolysate of buffalo's milk proteins was treated with methionine ethyl ester in the presence of α‐chymotrypsin during the EPM. Methionine content of this product was more than three times (5.4%) higher than that of the original buffalo milk protein (1.5%). The electrophoretic patterns of the modified proteins showed that the enzymatic reaction was mainly characterized by transpeptidation. Molecular masses of the modified protein fractions were influenced by the concentration of L‐methionine ethyl esters in the reaction mixture during the EPM. EPM products from the buffalo milk protein hydrolysates with α‐chymotrypsin and trypsin or with pepsin and trypsin showed low allergenic activities compared with those when buffalo milk proteins were hydrolyzed with α‐chymotrypsin or wi

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1995.tb00532.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe membrane associated enzyme phosphatidylinositol: ceramide phosphoinositol transferase (IPC synthase) catalyzes an essential step in the biosynthesis of yeast inositol‐containing sphingolipids. A variety of solubilization agents were examined for their ability to release IPC synthase activity from yeast membranes. The most effective solubilization agent was Triton X‐100 which released over 90% of the IPC synthase activity. The basic enzymological properties of the solubilized enzyme were determined using a Triton X‐100/phosphatidylinositol/ceramide/enzyme mixed micellar assay system. IPC synthase activity was dependent upon the surface concentrations of phosphatidylinositol and ceramide in a phosphatidylinositol/ceramide/Triton X‐100 mixed micelle. Maximal enzyme activity was measured at 30C and pH 7.0 in the presence of 5 mM Triton X‐100, 1 mM manganese and 5 mM magne

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1995.tb00533.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTVarious biochemical parameters measured in sockeye salmon, Oncorhynchus nerka, feeding in the Gulf of Alaska in July during the maturation process were contrasted with those obtained from mature sockeye salmon in Steep Creek, a small salmon stream near Juneau, Alaska. Degenerative changes in muscles, such as decrease in total lipid and protein contents in mature salmon were attributed both to the progressed activation of lipid hydrolytic enzymes and to autolytic activity, in addition to the inactivation of lipid and protein syntheses in muscle and liver. The depletion of lipid is associated with the energy utilization for migration and gonadal maturation as a result of the cessation of feeding.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1995.tb00534.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe acid‐solubilized collagen of lingcod skin has been extracted, purified and characterized. The skin collagen was readily solubilized by 0.5 M acetic acid, pH 2.5, treatment and further purified by fractional salt precipitation. The purified type I collagen had a melting temperature of about 20C, and its content in the skin of lingcod was high, as has the content of type I collagen been reported for land mammalian and avian skin. Analysis of the collagen by sodium dodecylsulfate‐polyacrylamide electrophoresis indicated the presence of three different α‐chains, α1, α2, and α3, which is the same structural composition of skin type I collagen found in Atlantic cod, Alaska pollack, blue grenadier and several other teleosts examined. The amino acid composition of lingcod skin type I collagen was very similar to the amino acid composition of Atlantic cod skin collagen, but was not strictly homologous with type I collagen from carp, invertebrate aquatic mammals and mammalian muscles. The purified collagen was radiolabeled to high specific radioactivity and used as a substrate for the assay of Pacific rockfish skeletal muscle matrix metalloproteinases. Radiolabeling did not show any apparent effect on the melting temperature or fibril formation properties of collagen. The radiolabelled lingcod type I collagen fibrils form at 15C and can be used to assay collagenolytic activity from fish at this te

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1995.tb00535.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTTwo heat‐stable metalloproteinases with collagenase activity have been identified in the skeletal muscle of Pacific rockfish (Sebastes sp.) and partially characterized. The 47 kDa and 95 kDa enzymes appear to be similar to mammalian matrix metalloproteinases (MMPs), with respect to molecular weight, pH‐activity profile, substrate specificity, dependence on calcium for activity, and inhibition‐activation profiles. The fish metalloproteinases readily hydrolyzed collagen and gelatin, but not β‐ or K‐casein, in SDS‐PAGE substrate zymograms. They also hydrolyzed collagen and gelatin in solution, but showed very low activity in solubilizing native fibrillar collagen. They did not hydrolyze solutions of β‐ or K‐casein, azocasein, hide powder azure or synthetic substrates for trypsin, chymotrypsin or collagenase. To our knowledge, this is the first report where fish muscle proteinases have been identified as possible members of the family of MMPs. The rockfish muscle MMPs appear to be different from other currently identified fish muscle proteinases in regard to molecular weight, substrate specificity and activation‐inhibition profiles. These two enzymes could be partly responsible for the degradation of collagen and other extracellular matrix proteins in fish muscle and for the texture softening

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1995.tb00536.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTActivities and some other properties of ascorbate oxidases (AAO) from the fruits of family Cucurbitaceae were investigated. The peel and the flesh of seven varieties had activities ranging between 35–56500 units/mg protein and 14–1250 units/mg protein, respectively. AAO from different varieties had a similar pH optimum of around 6–6.5 and a broad pH stability ranging from pH 5 or 6 to pH 10 or 11. These properties appear to be conserved in the AAO's from the family of Cucurbitaceae. The AAO's of melon cv. andes, kinsho and papaya were more susceptible to heat denaturation than AAO from pu

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1995.tb00537.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY