Caseins hydrolysis studies

Trieu-Cuot, P. and Gripon, J. C. 1981. Casein hydrolysis by Penicillium caseicolum and Penicillium roqueforti proteinases A study with isoelectric focusing and two-dimensional electrophoresis. Neth Milk Dairy J. 35, 353-357. 

Synthetic substrates allow rapid determination of the catalytic constants of an enzyme. Nevertheless, it is known that the environment of the peptide bond depends largely on physico-chemical conditions of the applied media, and imposed steric hindrance. Since these parameters are important, the hydrolysis of purified (3-casein was studied at different pHs. The kinetic analysis revealed that the mutant conserved the native trypsin capacity to hydrolyze peptide bonds containing arginyl and lysyl residues. The optimal pH of activity changed considerably according to the mutation. 

There is currently little understanding of the influence of interfacial composition and (nano)structure on the kinetics of enzymatic hydrolysis of biopolymers and lipids. However, a few preliminary studies are beginning to emerge (McClements et al., 2008 Dickinson, 2008). Thus, for example, Jourdain et al. (2009) have shown recently that, in a mixed5 sodium caseinate + dextran sulfate system, the measured interfacial viscosity increased from qs = 220 mN s m 1 without enzyme to qs = 950 mN s m 1 with trypsin present. At the same time, the interfacial elasticity was initially slightly reduced from (7S = 1.6 mN m 1 to (h = 0.7 mN m, although it later returned to close to its original value. Conversely, in the... 

In Table II are shown the results from kinetic studies with commercially available gastric and pancreatic enzymes. Trypsin was strongly inhibited, at least at a low concentration of casein as substrate. The hydrolysis of benzoyl arginine ethyl ester (BAEE) by trypsin was non-competitively inhibited, giving a 30% reduction of Vmax at 0.5 mg/ml of the LMW fraction. Carboxypepti-dase A, and to a lesser extent carboxypeptidase B, were non-competitively inhibited as well. Pepsin and chymotrypsin were not affected by the conditions used in these assays. 

Enzymatic gelation of partially heat-denatured whey proteins by trypsin, papain, pronase, pepsin, and a preparation of Streptomyces griseus has been studied (Sato et al., 1995). Only peptic hydrolysate did not form a gel. The strength of the gel depended on the enzyme used and increased with increasing DH. Hydrolysis of whey protein concentrate with a glutamic acid specific protease from Bacillus licheniformis at pH 8 and 8% protein concentration has been shown to produce plastein aggregates (Budtz and Nielsen, 1992). The viscosity of the solution increased dramatically during hydrolysis and reached a maximum at 6% DH. Incubation of sodium caseinate with pepsin or papain resulted in a 55-77% reduction in the apparent viscosity (Hooker et al., 1982). 

Modifications introduced by the mutations were central to the alteration of the specificities of the enzymes studied, which were capable of cleaving (3-casein at many new sites, for example, hydrolyzing the fragment Argl-Lysl05, reported to be a trypsin inhibitor (Bouhallab et al, 1997). Since many tryptic inhibitors contain amidated Glu and Asp, and form amyloid structures, the mutants of this type could be used for the hydrolysis of the lytically resistant protein structures. 

In addition, peptides binding different minerals have been found in whey proteins, i.e., from (3-lg, a-la and LF. Since these proteins are not phosphorylated, the minerals seem to bind through other binding sites than caseins. Seventeen (17) different peptides have been identified by hydrolysis of (3-lg with thermolysin using two different concentrations of calcium. Also, peptides from a-la and LF using trypsin, chymotrypsin or pepsin have been reported. Studies with 3-lg and a-la peptides have shown a higher affinity for iron than the native proteins (Vegarud et al., 2000). 

Plasmin Hydrolysis of /3-Casein. Studies on the susceptibility of partially methylated /3-casein to cleavage by trypsin-like enzymes were carried out using the enzyme porcine plasmin. In preliminary investigations, we confirmed that the y-caseins produced by plasmin hydrolysis of native /3-casein were identical with those occurring naturally (28). These are designated yi-, y2-, and y3-casein according to the nomenclature recommendations of Whitney et al. (29) and correspond to residues 29-109, 106-209, and 198-209 of -casein. Presumably the proteose peptone products of plasmin hydrolysis are identical with their natural counterparts, but the latter were not available for comparison. 

Plasmin Hydrolysis of 14C-Methyl-/3-Casein. On the basis of a study by Ottesen and Svensson (2), which described the relative amounts of mono- and dimethyllysinyl derivatives produced by reductive methyla-... 

The results on the hydrolysis of partially methylated /3-casein by plasmin indicate that proteins radiomethylated to a low level can serve as substrates for trypsin-like enzymes and probably for proteinases in general. Because it is likely that methylation will interfere with enzymatic attack at lysine residues, the complete hydrolysis of /3-casein probably would not be possible. Studies on mastitic milk demonstrate the usefulness of 14C-methyl proteins for qualitative examination of protein hydrolysis in complex multiprotein systems where resolution and characterization of individual protein fragments is difficult. The requirements in such studies are the availability of pure samples of the proteins under investigation and a suitable technique for separating the radio-labeled protein from hydrolytic products. 

This work was supported in part by Ross Laboratories (Columbus, OH), the College of Agricultural and Life Sciences, University of Wisconsin—Madison, the Cooperative State Research Service, USD A, and by the Irish Agricultural Institute. T. Richardson was a Fulbright-Hays Scholar at the Agriculural Institute in Fermoy, County Cork, Ireland, where the hydrolysis of methylated /3-casein by plasmin was studied. The authors are grateful for helpful discussions with L. K. Creamer. 

Hydrolysis of the Isopeptide Bond. The bio availability of methionine covalently linked to casein has been studied by the response (protein efficiency ratio) of rats that have been fed the modified protein (23,63). The covalently bound methionine appears to be as available as the free amino acid. This finding indicates that there is an efficient enzymatic... 

Heat and alkaline treatments have been known since the early part of the century to raoemize amino acid residues in proteins (1,2,). Dakin and Dudley (3) also studied digestibility of casein in vitro and in vivo after hydroxide treatment. Heating casein with 0.5 N NaOH at 37° for about 30 days completely prevented enzymatic hydrolysis and intestinal absorption when the treated casein was fed to a dog. The kinetics of base-catalyzed racemization of proteins was investigated by Levene and Bass (4-6). In these early studies, the extent of racemization was measured by changes in optical rotation. 

Many workers have studied the influence of enzymatic hydrolysis on the functional properties of various food proteins, and much of this work has recently been reviewed by Richardson (2). However, there seem to be very few reports which quantitatively relate functionality to parameters which characterize the protein hydrolysates per se (e.g. molecular weight). Ricks et al. (3 ) examined the solubility and taste of a number of pure proteins (denatured pepsin, lactoblobulin, a-Sj -, K-, and 8-casein) hydrolysed with... 

Tryptophan was first isolated only at the beginning of this century (411). A number of color reactions of proteins were extensively studied in the latter half of last century and numerous attempts were made to isolate the chromogen responsible. The name tryptophan was given to this chromogen in 1890 by Neumeister (645). The chromogen was soon associated with the substance giving rise to indole on bacterial putrefaction of proteins. The failure of many early attempts to isolate tryptophan was probably due to the fact that it is destroyed on acid hydrolysis. The successful isolation by Hopkins and Cole (411) used enzymic hydrolysis of casein, but the chief reasons for their success were their discovery of mercury salts as... 

There have been a limited number of studies on the effects of enzymic modification of protein concentrates on functional properties other than solubility. Studies on functional properties, as modified by enzymic treatments, emphasize foam formation and emulsifying characteristics of the hydrolysates. Treatment of chicken egg albumen alters the functional properties of the egg proteins in terms of foam volume and stability and the behavior of the proteins in angel food cakes (25). Various proteolytic enzymes were used to degrade the egg albumen partially. However, proteolytic enzyme inhibitors indigenous to the egg proteins repressed hydrolysis of the egg proteins compared with casein. 

K-casein by lithium borohydride yielded an insoluble p-/c-casein and a macropeptide similar to that from rennin action. The presence of phenyl-alanol in the precipitate suggested phenylalanine as the C-terminal residue in p- -casein (166). Early work failed to detect an N-terminal residue in the macropeptide (2). However, limited acid hydrolysis of the macropeptide allowed the detection of a very labile N-terminal methionine which had previously escaped detection as a result of destruction during hydrolysis (167). The existence of an N-terminal methionine in the macropeptide was subsequently confirmed (168). The existence of the rennin-susceptible Phe-Met bond was also demonstrated from studies on the primary sequence of /c-casein (see Figure 6). 

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