Pepsin components

Carmichael DJ, Dodd CM and Veis A (1977) The solubilization of bone and dentine collagens by pepsin. Effect of cross-linkages and non-collagen components. Biochim Biophys Acta 491, 177-192. 

The membrane surface may become passivated by some solution components that are strongly adsorbed. This effect is often encountered in measurements on biological fluids containing proteins. These adsorption effects can sometimes be prevented by selecting a suitable compoation of the sample and standard solutions for example by adding trypsin and triethanolamine to dissolve proteins [108]. Passive electrodes can sometimes be reactivated by soaking in suitable solutions (for example pepsin in 0.1M HCl [68]) and in more serious cases the membrane must be replaced or a solid membrane be repolished. 

Iodination of PIR (147) showed 1 residue buried, Tyr 25, and all others iodinated at least to the monoiodotyrosyl form. Pepsin-inactivated RNase also has only one abnormal tyrosyl by titration which is thus assumed to be 25. Iodination of RNase-S is very similar to RNase-A in the early stages (lift). Extensive iodination leads to dissociation of the protein and peptide components. Direct iodination of S-protein indicated that all 6 tyrosyl residues were accessible, in this sense comparable to urea-denatured RNase-A. Substantial structural changes must be involved for both S-protein and PIR if Tyr 97, in particular, is to become susceptible to attack (see Section IV,B,3). 

Enzymes are protein catalysts of remarkable efficiency and specificity. Lipid, carbohydrate, nucleotide, or metal-containing prosthetic groups may be attached to these enzymes and serve as essential components of their catalyses by enhancing specificity and/or stability (8—13). Each enzyme has a specific temperature and pH range where it functions to its optimal capacity the optima for these proteins usually He between 37—47°C, and pH optima range from acidic, ie, 1.0 in the case of gastric pepsin, to alkaline, ie, 10.5 in the case of alkaline phosphatase. However, enzymes from extremely thermotolerant bacteria have become available these can function at or near the boiling point of water, and therapeutic use of these ultrastable proteins can be anticipated. 

A better understanding of the structure of collagen IV molecules explains some previous observations. The occurrence of the 7 S domain and nonhelical interruptions in the molecule can explain in part the heterogeneous mixture of collagenous components isolated from basement membrane, particularly when pepsin or other proteases are used to solubilize the protein. The molecules isolated from lathyritic basement membrane by acid extraction are truncated and lack the 7 S domain presumably due to cleavage by endogenous proteases. 

Bovine haemoglobin, the protein from erythrocytes which occurs as a minor component in meat and meat products, is also a precursor of opioid peptides (haemorphins). These opioid peptides are released by pepsin digestion in vitro and may also be produced by macrophages. Moreover, haemorphins have been found to decrease the tension of the guinea pig ileum in vitro (Nyberg et al., 1997). 

Hydrolytic activity of pepsin is maximal at pH 2-3, the stomach pH, and aspartate is an essential component of the active site. Pepsin is inactive at pH 7. Which enzymatic reaction mechanisms is most likely of major importance in the action of pepsin ... 

HIV-P is a symmetrical homodimer of identical 99 residue monomers, structurally and mechanistically similar to the pseudosymmet-ric pepsin family of proteases (92-94), whose members include renin. Because the protease is a minor component of the virion particle, intensive structural studies required overproduction through recombinant DNA methods. One of the first structures was determined with material synthesized nonbiologically (through peptide synthesis). As of June 2002, there were over 100 X-ray structures repre-... 

It has been shown that the intramolecular links in /3-components are split by heat or mild alkali treatments (Chun and Doty, 1958 Doty and Nishihara, 1958 Kiihn et at., 1963b), although this action is rapidly followed by a more general breakdown (Altgelt et al., 1961 Schleyer, 1962). A similar cleavage by pepsin and trypsin has been reported by Kiihn (Kiihn et al., 1963a) and by Schmitt (Rubin et al., 1963), whereas it was not found by Hafter and Hermann (1963). 

For many years, the facility of the hydrochloric acid assay in gastric juice and the unavailability of good quantitative techniques for fractionation of proteins and mucosubstances have directed the interest of researchers toward the study of hydrochloric acid in the stomach. The only other material in gastric juice, studied and quantitated for many years and representative of the nondialyzable gastric secretory products, was pepsin. Study of other large molecular components has been hampered by the complexity of gastric juice, technical diflSculties encountered in its fractionation, and lack of adequate quantitative methods for the assay of these materials. 

A third proteinase appears to exist in the gastric juice, which exerts proteolytic activity at a neutral pH of about 7.0, i.e., in the range where pepsin and cathepsin no longer are active. The existence of a protease called parachymosin, active at pH 5.0-7.0, has been described in the past (Fig. 1) (see B46). Buchs (JM6) considered it to be an integral part of the gastric protease, the two other components of which were pepsin and cathepsin. In the early thirties, Castle s group found some paral-... 

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