Pepsin significance

The mechanism by which sucralfate accelerates healing of duodenal ulcers has not been determined. It does not have significant antisecretory, acid neutralizing activity or direct stimulation of ulcer healing. It is known that the mechanism is local rather than systemic. Binding of pepsin or bile salts may contribute to its effect. It is indicated for the short-term therapy of active duodenal ulcers and for maintenance at reduced dosage. 

Pepsin consists of a single polypeptide chain of molecular weight 34 644 and 327 amino acid residues. Ser-68 is phosphorylated, but this phosphate may be removed without significantly altering the catalytic properties of the enzyme. As in other acid proteases, the active site is an extended area that can accommodate... 

Serine/threonine kinase activity has been reported in ESP of pepsin-HCl isolated muscle larvae (Arden el al., 1997) and kinase activity was associated with proteins of 70 and 135 kDa. Phosphorylation status is functionally significant for multiple regulatory factors, including those involved in muscle differentiation (Li et al., 1992). Therefore, kinase activity in parasite secretions may be significant in either the muscle or intestinal phases of infection. 

Kirchgessner and Steinhart (52) studied the in vitro digestion of soy protein isolate with pepsin. They showed that a relatively higher percentage of the essential amino acids threonine, valine, isoleucine, leucine and phenylalanine were found in the undigested residue and therefore would be present in lower proportions in the hydrolysate. Myers et al. ( ) hydrolyzed a soy protein isolate with a fungal acid protease. They also found that the essential amino acid content of the hydrolyzate was lower than the isolate, but, as prepared by their continuous process, the hydrolyzate PER was not significantly reduced as compared to the isolate PER. 

Emmons (1970) experienced significant inactivation when commercial pepsin and pepsin-calf rennet mixtures were diluted with high-pH, hard water 10 min before adding them to the cheese vat. Mickelsen and Ernstrom (1972) reported that mixtures of porcine pepsin and calf rennet were stable between pH 5.0 and 6.0, but that pepsin activity was lost from the mixture aboire pH 6.0. This loss was shown to be entirely due to pepsin instability. Below pH 6.0 chymosin activity was destroyed by pepsin. 

Green (1972) reported that Cheddar cheese made entirely with bovine pepsin was only slightly inferior to that made with calf rennet and Fox and Walley (1971) found no significant difference between Cheddar cheese made with bovine pepsin and rennet. Fox (1969) found that the milk-clotting activity of bovine pepsin is less pH-dependent than that... 

Linklater, P. M. 1961. The significance of rennin and pepsin in rennet. Ph.D. Thesis. Univ. of Wisconsin, Madison. 

This approach has been applied extensively to peptidases, as the substrate or inhibitor structure can be varied most liberally. Correlations between inhibitor K and substrate Ku/kcat have been demonstrated for the phosphorus-containing peptide inhibitors of thermolysin (Figure 9.3) (Bartlett, 1983 Morgan, 1991), carbox-ypeptidase A (Hanson, 1989), and pepsin (Bartlett, 1996). Each series of inhibitors shows a slope close to unity in the log K vs. log (KM/kcat) plot importantly, the structural variations at the P2 residue should not affect kuncat significantly. 

The effect of the dissociation of the [3-carboxyl group of Asp77 in double mutated pepsin on the recognition of Lys residue at the Pi position were examined by pH-dependent hydrolysis of two type of peptide substrates containing Phe or Lys at Pi. The major differences in pH activity profiles were the kcJKm values below pH 4. These values for Pi substrates (peptide B and C) decreased as the pH dropped, while there was no significant change for Pi substrate (peptide A). The Km values were pH independent in all cases. These results are different from those of the studies that the existence of Lys or Arg residues at the P4, P3, P2, P3 , P4 , and P5 positions in the substrates influences the Km values with little effect on kcat in porcine pepsin [41] the ionic interactions between the basic residues in the substrate and the side-chain carboxylates in the S4, S3, S2, S3 , S4 , and S5 subsites contribute to substrate affinity. 

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