Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.7 (plasmin)
 9,023 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A method was investigated for the sensitive radiochemical assay of milk protein transformations. beta-Casein was reductively methylated with NaBH4 and H14CHO giving a product of spec. act. 4.42 microCi/mg in which a maximum of 12% of the lysine residues were labelled. Methylation did not alter the electrophoretic or chromatographic properties of the protein, or its pattern of proteolysis by plasmin. The substrate susceptibility of 14C-methylated beta-casein towards plasmin was determined by measuring radioactivity transfer to the proteolytic fragments gamma 2- and gamma 3-casein. Compared with the native protein, no decrease in substrate susceptibility was detected. The presence in milk of the plasmin-like enzyme, milk proteinase, was demonstrated and its activity at 4 degrees C was quantified by examination of the fragmentation pattern of added 14C-methylated beta-casein. It was concluded that 14C-methylated protein substrates, prepared by reductive methylation, are well suited to the study of hydrolytic enzymes and that they can provide valuable information on milk protein transformations. In particular, no interference was encountered with the rate of cleavage by plasmin when the level of methylation was kept to a minimum.
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PMID:14C-Methylated beta-casein as a substrate for plasmin, and its application to the study of milk protein transformations. 645 Jun 17

The addition of potassium iodate to milk at 9.1 mM before UHT treatment resulted in rapid breakdown of alpha s- and beta-casein during subsequent aseptic storage. Maximum rates of proteolysis were observed at storage temperatures of 37-45 degrees C, but the reaction was strongly inhibited by storage at 55 degrees C and by increased holding time at 140 degrees C during the UHT sterilization. Iodate-induced proteolysis of purified alpha s1-and beta-casein was detected only with solutions in the serum phase of raw milk; no proteolysis occurred with solutions in 0.1 M-phosphate buffer (pH 6.7) or in milk ultrafiltrate, irrespective of whether whey proteins and lactose were also added. Thus, it appears that iodate increased the activity of one or more proteolytic components which were present in milk and were unable to pass through an ultrafiltration membrane. However, it is unlikely that iodate acts by increasing the activity of proteinases produced by contaminant bacteria; the presence of iodate did not affect the activity of a proteolytic enzyme isolated from Pseudomonas fluorescens PM-1. Furthermore, iodate promoted protein breakdown during storage of milk drawn aseptically from the cow and subsequently UHT processed. It is suggested that iodate increased the activity of native milk proteinases, other than plasmin which was inactivated by UHT treatment, possibly by preventing thiol-disulphide exchange reactions during the heating process.
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PMID:Effects of adding potassium iodate to milk before UHT treatment. ii. iodate-induced proteolysis during subsequent aseptic storage. 702 16

Five British Saanen goats were milk sampled during the first 39 weeks of lactation to determine changes in casein composition. Caseins were separated by anion- and cation-exchange FPLC to determine the relative amounts of the individual caseins. Acid, alkaline and SDS-PAGE were used to determine possible genetic polymorphisms and observe any lactational changes. Total casein nitrogen was determined using a micro-Kjeldahl method and this allowed the concentrations of individual caseins to be calculated. The milk of one animal, which had the deduced genotype alpha s1-CnAB, showed higher concentrations of both total and alpha s1-casein. The remainder of the group were either heterozygous alpha s1-CnBE or, more probably, homozygous alpha s1-CnE and produced milk of a generally lower protein concentration. Both FPLC and PAGE results showed that the relative amounts and concentrations of alpha s2-casein decreased with stage of lactation, consistent with its susceptibility to proteolysis. The relative amounts of the breakdown products of plasmin attack on beta-casein, gamma-caseins, were highly negatively correlated with milk yield (r = -0.942, P < 0.001) in the declining phase of lactation, reflecting the gradual involution of the gland at this time. The relative amount of kappa-casein increased by approximately 50% after peak lactation and its concentration almost doubled near the end of lactation. These compositional changes may alter the processing qualities of goats' milk in relation to cheese production.
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PMID:Changes in casein composition of goats' milk during the course of lactation: physiological inferences and technological implications. 759 29

The whole N fraction of six samples of hard and semi-hard pressed cheeses was analysed using PAGE, polyacrylamide gel isoelectric focusing and immunoblotting with polyclonal antibodies against beta- and alpha s1-casein. The origin of some electrophoretic bands corresponding to peptides produced from the enzymic degradation of the casein fractions was established. A number of these peptides were also present in the in vitro hydrolysates of casein with plasmin and chymosin. Thus, it was also possible to determine which casein was the source of each peptide and which enzymes were active in cheese. Compared with the traditional Coomassie staining procedures, immunoblotting is more sensitive and specific, making the interpretation of each electrophoretic profile easy. Thus, it was also possible to obtain a clear picture of the state of each casein fraction in a cheese variety. Two main peptides were isolated from the pH 4.6-insoluble N fraction of Parmigiano-Reggiano using DEAE-cellulose chromatography and identified, from the amino acid sequence of the N- and C-terminal ends, as gamma 3-casein (beta-casein(f108-209)) and alpha s1-PL1 (alpha s1-casein(f80-199). In both cases, a Lys-X bond was hydrolysed, indicating the action of a trypsin-like enzyme in beta- and alpha s1-casein hydrolysis during the ripening of this variety of hard pressed cheese.
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PMID:Gel electrophoresis and immunoblotting for the detection of casein proteolysis in cheese. 760 74

The objective of this study was to determine the response of individual milk proteins to a reduction in amino acid (AA) availability induced by atropine and to determine whether the response was different in cows with different beta-lactoglobulin (LG) phenotypes. Six cows that were homozygous for the A variant of beta-LG and six cows that were homozygous for the B variant of beta-LG were each given a single subcutaneous injection of saline or 20 mg of atropine. In both groups of cows, atropine decreased milk yield by 30% and reduced the concentration of alpha-lactalbumin (LA) by 25 to 30% at 8 h following injection. Eight hours after atropine injection, yield of beta-LG was 41% lower than it was following saline injection, and yield of beta-casein (CN) after atropine injection declined 16% relative to saline. Concentrations of BSA and the ratio of gamma-CN to beta-CN, which reflects plasmin activity in milk, were significantly increased after administration of atropine. Although the response to atropine tended to be more pronounced in cows that were homozygous for beta-LG B, they were not significantly different from the response of cows that were homozygous for beta-LG B, they were not significantly different from the response of cows that were homozygous for beta-LG A. The differential response of individual proteins to a reduction in AA concentrations in whole blood suggested that susceptibility to restriction in substrate availability differed for individual proteins. The concentration of lactose in plasma did not change, which implied that the integrity of the mammary epithelial barrier was not compromised when AA derived from blood were diminished. The consistent concentration of lactose combined with the minimal increase in total yield of BSA in milk following atropine treatment indicated that the increased concentration in milk of proteins derived from serum was due to the concentrating effect of lower milk volume.
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PMID:Effect of atropine on milk protein yield by dairy cows with different beta-lactoglobulin phenotypes. 924 90

Several peptides were isolated from the diafiltration retentate, prepared using 10 kDa membranes, of the water-soluble extract from a commercial mature Cheddar cheese and identified by amino acid sequencing and mass spectrometry. Most of the peptides were from the N-terminal half of the beta-casein, but peptides from alpha s1- and alpha s2-caseins were also identified; the extract also contained alpha-lactalbumin. Identified peptides showed the important role played by lactococcal cell envelope proteinases in the degradation of primary proteolytic products from alpha s1- and beta-caseins, produced by chymosin and plasmin respectively. Plasmin seemed to be involved in the hydrolysation of alpha s2-casein. Several phosphopeptides were identified and the action of phosphatase on these peptides was evident.
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PMID:Isolation and identification of further peptides in the diafiltration retentate of the water-soluble fraction of Cheddar cheese. 927 58

The proteolytic activity of plasmin on soluble caprine beta-casein (CN) was studied in 50 mM Tris.HCI buffer, pH 8.0, at 37 degrees C. Electrophoretic studies showed that hydrolysis of this protein results in an electrophoretic pattern that is similar to the pattern obtained from plasmin hydrolysis of bovine beta-CN (gamma-CN and complementary N-terminal fragments), suggesting that plasmin probably attacks the same regions that are susceptible to cleavage in bovine beta-CN. As determined by SDS-PAGE, the gamma-like components of caprine milk consisted of two fragments with relative molecular mass of 9200 and two with relative molecular mass of 21,400 that could differ in the level of phosphorylation. Apparently, the high molecular mass components are homologous to bovine beta-CN (f 29-209) (gamma 1-CN), and the low molecular mass components are homologous to bovine beta-CN (f 106-209) and beta-CN (f 108-209) (gamma 2- and gamma 3-CN). Complementary N-terminal fragments had values for molecular masses in the range 13,600 to 8500 and urea-PAGE patterns that were more complex than those obtained in bovine casein because of the different phosphorylation levels in caprine beta-CN. These fragments were also present in the hydrolysate of whole caprine casein that had been treated with plasmin.
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PMID:Hydrolysis of caprine beta-casein by plasmin. 936 Nov 97

Proteolytic activity in mammary gland secretions is associated with hydrolysis of secretory proteins during involution. Peptides generated from hydrolysis of milk proteins were characterized in secretions from the bovine mammary gland during involution to understand the fate of the milk proteins better. Mass spectral analysis of mammary secretions showed numerous peptides ranging between 0.7 and 14 kDa during mammary involution, but these peptides were not observed in normal milk. Mass spectral profiles representing discrete peptide fragments were similar on d 7, 14, and 21 of involution, suggesting that milk proteins were only partially hydrolyzed during involution. N-Terminal amino acid sequences of four peptides indicated that they were produced by hydrolysis of beta-casein during involution and probably resulted from plasmin hydrolysis. A 20-kDa peptide was identified as a fragment of a 39-kDa protein that was previously identified in bovine mammary secretions during involution. Mass spectral analysis of lactoferrin isolated from mammary secretions during involution showed major hydrolytic products. Immunoblot analysis confirmed that lactoferrin that was isolated from mammary secretions during involution contained a number of hydrolytic products. Intramammary hydrolysis of milk proteins by plasmin probably leads to the generation of the discrete peptides observed in the mammary secretions and contributes to the fate of these proteins during involution of the bovine mammary gland.
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PMID:Peptides generated from milk proteins in the bovine mammary gland during involution. 956 78

To investigate structure-function relationships with regard to emulsion-stabilizing properties, peptides from bovine beta-casein (betaCN), obtained by plasmin hydrolysis and fractionation of the hydrolysate, were isolated and identified on the basis of their masses determined by electrospray ionization mass spectrometry, the primary structure of the intact protein, and the known specificity of the enzyme. An amphipathic peptide fraction was fractionated further by ion-exchange chromatography and subsequent hydrophobic interaction chromatography resulting in the components betaCN[f 1-105/107] and betaCN[f 29-105/107]. The latter peptides had poor emulsion-stabilizing properties compared to the former ones, and the stability of an emulsion formed with betaCN[f 29-105/107] was also more sensitive to hydrophobic impurities than that of an emulsion formed with betaCN[f 1-105/107]. The highly charged N-terminal part appeared to be important for the emulsion-stabilizing properties of these peptides. A hypothesis for the structure-function relationship is given.
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PMID:Functionality of beta-casein peptides: importance of amphipathicity for emulsion-stabilizing properties. 1055 62

Stress and stress related hormones such as glucocorticoids inhibit lactation in cows. In the present study we propose a novel mechanism connecting stress with plasminogen-plasmin system (PPS) (an enzymatic mechanism in milk, which leads to the breakdown of the major milk protein casein). We show that stress activates the PPS leading to an increase in plasmin activity, and that a distinct plasmin-induced beta-casein breakdown product (fraction 1-28) is a potent blocker of potassium channels in mammary epithelia apical membranes. The reduction in milk production due to dehydration stress or glucocorticoid (dexamethsone) was correlated with the activities of plasmin and channel blocking activity in the milk of the tested cows. The notion that the axis Stress-PPS-beta-casein fraction 1-28 is responsible for the reduction in milk yield is supported by the results of experiments showing that injecting solution composed of casein digest enriched with beta-casein fraction 1-28 to the udder lumen leads to a transient reduction in milk production. Furthermore, injecting a pure beta-casein fraction 1-28 to the udder lumen of goat's lead also to a transient reduction in milk production with kinetics that was similar to the kinetics observed in cows.
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PMID:Stress down regulates milk yield in cows by plasmin induced beta-casein product that blocks K+ channels on the apical membranes. 1104 1


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