Caseins residues

Macropeptides from K-casein. These peptides represent the C-terminal region of K-casein (residues 106-169) which is released by rennet during the manufacture of cheese or rennet casein (Chapter 10). The (glyco)macropep-tides are released into the whey which contains 1.2-1.5gl S and from which they can be readily recovered, e.g. by anion exchange using Spherosil QMA resin. The peptides contain no Phe, Tyr, Trp or Cys the absence of aromatic amino acids makes the macropeptides suitable for the nutrition of patients suffering from phenylketonuria. 

FIG. 2 Helical wheel structures of (a) Os,-casein residues 12-23 (b) bovine serum albumin residues 383-396 (c) bovine serum albumin residues 541-555 (d) P-lacto-globubn residues 125-143 and (e) synthetic peptide H. Hydrophobic amino acids are shown by closed circles, hydrophUic charged amino acids by open circles, and hydro-phibc uncharged amino acids by shaded circles. (From Ref. 5.)... 

Antimicrobial peptides are effective against different bacteria and yeasts. An example of an antimicrobial peptide is lactoferricin, which includes residues 17-41 from lactoferrin. Other peptides with antimicrobial properties are isracidin, derived from casein (residues 1-23), and casocidin-I, as a result of hydrolysis ofa32"Casein (residues 150-188). Lactoferricin also has immuno-and cytomodulatory properties that similarly show a number of peptides arising by hydrolysis of milk caseins and serum proteins. 

Soybean Protein Isolates. Soybean protein isolates, having a protein content of >90 wt%, are the only vegetable proteins that are widely used in imitation dairy products (1). Most isolates are derived from isoelectric precipitation, so that the soybean protein isolates have properties that are similar to those of casein. They are insoluble at thek isoelectric point, have a relatively high proportion of hydrophobic amino acid residues, and are calcium-sensitive. They differ from casein in that they are heat-denaturable and thus heat-labile. The proteins have relatively good nutritional properties and have been increasingly used as a principal source of protein. A main deterrent to use has been the beany flavor associated with the product. Use is expected to increase in part because of lower cost as compared to caseinates. There has been much research to develop improved soybean protein isolates. 

Over 30 amino acids have been identified in the hydrolysis product of casein of which glutamic acid, hydroxyglutamic acid, proline, valine, leucine and lysine comprise about 60%. The residues of the aminoacid arginine also appear to be of importance in the cross-linking of casein with formaldehyde. 

Casein is the only protein that has achieved commercial significance as a plastics raw material. Many other proteins are readily available in many vegetable material residues which arise from such processes as the extraction of oils and starches from seeds. It would be advantageous to countries possessing such residues if plastics could be successfully exploited commercially. Although plastics materials have been produced they have failed to be of value since they are invariably dark in colour and still have the water susceptibility and long curing times, both of which are severe limitations of casein. 

FIGURE 8.13 SEC of casein hydrolyzates. Numbers above the peaks refer to the number of amino acid residues in the typical peptide in the indicated fraction. Column PolyHEA, 200 X 9.4 mm 5 /zm, 200 A. Flow rate 0.5 ml/min. Mobile phase 50 mtA Formic acid. Detection A250. Samples (A) Pancreatin hydrolyzate and (B) tryptic hydrolyzate. (Adapted from Ref. 29 with permission from Silvestre et of. Copyright 1994, American Chemical Society.)... 

PHOSPHOPROTEINS. These proteins have phosphate groups esterified to the hydroxyls of serine, threonine, or tyrosine residues. Casein, the major protein of milk, contains many phosphates and serves to bring essential phosphorus to the growing infant. Many key steps in metabolism are regulated between states of activity or inactivity, depending on the presence or absence of phosphate groups on proteins, as we shall see in Chapter 15. Glycogen phospho-rylase a is one well-studied example. 

HSFl phosphorylation must be sensitive to nonheat inducers of HSF-DNA binding activity because HSFl phosphorylation can be achieved at 37 °C by other inducers of the HS response. HSF 1 contains polypeptide sequences that could serve as substrates for well characterized protein kinases, but few of these are known to be heat inducible. One family of protein kinases, the S6 protein kinases, have already been shown to exhibit heat inducible activity however, their peak level of activity during HS occurs well after the maximal induction of HSF phosphorylation (Jurivich et al., 1991). Thus, other protein kinases are likely to be directly linked to the phosphorylation of HSF. Some of the putative protein phosphorylation sites on HSF include motifs for protein kinase C, casein kinase, and enterokinase. There are tyrosine sequences that match substrates for known tyrosine kinases, but whether these residues are accessible to phosphorylation is not established. 

In an attempt to design the p-turn-peptide-mimics, aspartic acid (an amino acid also known as aspartate) and lysine (an amino acid especially found in gelatin and casein) were attached to each amine group of 1,3-diaminoada-mantane in the form of amide bonds. The term p-turn refers to a peptide chain that forms a tight loop such that the carbonyl oxygen of one residue is hydrogen... 

Type Portion of total caseins (%) Molecular weight (kDa) Amino acid residues... 

The six major proteins of milk, asl-, o s2-, and /c-casein, jS-lactoglobulin, and a-lactalbumin, contain at least one tryptophan residue [57], the fluorescence of which allows the monitoring of the structural modifications of proteins and their physicochemical environment during the coagulation processes. Emission fluorescence spectra of the protein tryptophanyl residues were recorded for the milk coagulation kinetics induced by... 

Activation of cells results in the release of IKB, followed by the rapid proteolysis of IKB. Although phosphorylation of serine 32 and 36 in the amino-terminal part of IKBa occurs when the proinflammatory cytokines or mitogens are administered to a T lymphocytic cell line, a different site of action has been found after H2O2 incubation (Schoonbroodt et al., 2000). The tyrosine residue 42 and the C-terminal PEST (Pro-Glu-Ser-Thr) domain plays a major role in the phosphorlylation of IKB after treatment with H2O2. Furthermore the CVinducible phosphorylation was not dependent upon IKB kinase activation but involved casein kinase II. The importance of iron for the activation of NFKB was underlined by the fact that... 

South Uist in the Outer Hebrides. A number of positive results were obtained and these compared well with the analysis of the fatty acids. However, some samples gave a negative result for ocsl-casein but a positive one for milk fat based on the A13C value. The possibility exists that some of the residues represent sheep milk (which would give a negative result for bovine asi-casein), or that in some cases the casein molecule is degraded with consequent depletion of the immunological response. 

Whole milk (2 litres) is diluted with an equal volume of water at 30°-40° and commercial rennet (0-1 g.), dissolved in a few cubic centimetres of water, is added. The mixture is then left at the same temperature until separation of the casein is complete (about two hours). The whey is filtered through a filter cloth, and after the liquid has run off the residue is pressed down well. The casein, which contains a great deal of fat, is ground in a mortar with a little 1 per cent sodium hydroxide solution 1 to 1-5 litres of sodium hydroxide solution of the same concentration are then poured on to the resulting paste, and the mixture is gently warmed in a porcelain basin until all but the fat dissolves. 

No cysteine residues are found for alpha(sl) and P-caseins do. If any S-S bonds occur within the micelle, they are not the driving force for stabilization. Caseins are among the most hydrophobic proteins, and there is some evidence to suggest that they play a role in the stability of the micelle. It must be remembered that hydrophobic interactions are very temperature sensitive. 

In addition to CKle, a second casein kinase 1 orthologue, CK1(5, has been implicated in the mammalian circadian clock. CK15 and CKle both bind and phosphorylate mammalian PER proteins in vitro (Keesler et al 2000, Vielhaber et al 2000, Camacho et al 2001), and are physically associated with PER and CRY in vivo (Lee et al 2001). In tau mutants, PER proteins continue to be phosphorylated in spite of the lowered function measured for CKle in vitro (Lee et al 2001). It has been suggested that the residual phosphorylation might be supplied by PER-associated CK15 in the mutants, and that CKle and CK1(5 have overlapping functions in the mammahan circadian system (Lee et al 2001). 

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