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B Kassell

Publications and source records attributed to B Kassell.

5 recordsLinked to original sources
PubMed1977

Improved pepsin inhibitor derived from activation peptide 1-16 of porcine pepsinogen.

The peptide Leu-Val-Lys-Val-Pro-Leu-Val-Arg-Lys-Lys-Ser-Leu-Arg-Gln-Asn-Leu, a known pepsin inhibitor, is derived from the first 16 amino acids of porcine pepsinogen. It was prepared from the activation mixture and was modified by guanidination of its three lysine residues to form homoarginine residues. The modified peptide is a better pepsin inhibitor than the native peptide; for 50% inhibition of the milk clotting action of pepsin at pH 5.3, the molar ratio of peptide to pepsin required is 9 for the native inhibitor and only 2 for the guanidinated inhibitor. The dissociation constants (k1) of the inhibitor-pepsin complexes are 7 X 10(-8) and 1.4 X 10(-8) M for the native and guanidinated peptides, respectively. The guanidinated peptide is more resistant to digestion by pepsin at pH 3.5. The native and modified peptides partially protect pepsin from inactivation at pH 7. Stepwise removal of the amino-terminal Leu-Val-Har residues from the guanidinated inhibitor by Edman degradation decreases the pepsin-inhibiting activity only slightly at the first step, but markedly at the second and third steps. Thus, all of the amino-terminal sequence except the leucine residue is necessary for full activity.

Amino Acids↗
PubMed1977

Chemical modification of a pepsin inhibitor from the activation peptides of pepsinogen.

The peptide comprising the first 16 amino acids of porcine pepsinogen, prepared from the activation mixture, has been modified by guanidination of its three lysine residues to form homoarginine residues. The modified peptide is a better pepsin inhibitor than is the native peptide; for 50% inhibition of the milk-clotting action of pepsin at pH 5.3, the molar ratio of peptide to pepsin required is 9 for the native inhibitor and only 2 for the guanidinated inhibitor. Stepwise removal by Edman degradation of the amino-terminal Leu-Fal-Homoarg residues from the guanidinated inhibitor decreased the activity slightly at the first step and markedly at the second and third steps. Thus, all of the amino-terminal sequence except the leucine residue is necessary for full activity.

Amino Acid Sequence↗
PubMed1975

Oxidation of methionine residues of porcine and bovine pepsins.

By treating porcine and bovine pepsins with H2O2 at pH 3.2, 3.5 of the 4 methionine residues of porcine pepsin and 1.6 of the 3 residues of bovine pepsin were oxidized to methionine sulfoxide. The effect of modification on activity varied with the substrate. There were no significant changes in catalytic constants in the hydrolysis of acetyl-L-phenylalanyl-L-tyrosine by both pepsins and in the hydrolysis of benzyloxycarbonyl-L-glutamyl-L-tyrosine by porcine pepsin. Hydrolysis of benzyloxycarbonyl-L-glutamyl-L-tyrosine by bovine pepsin was too slow to measure. With benzyloxycarbonyl-L-histidyl-L-phenylalanyl-L-tryptophan ethyl ester as substrate, the modification decreased the catalytic efficiency (kcat/Km) by two-thirds for porcine pepsin and by half for bovine pepsin. With hemoglobin substrate, digestion was significantly less than with native pepsin for modified porcine pepsin, and slightly less for modified bovine pepsin. The results are interpreted as indicating the presence of a methionine residue that participates in the binding of long substrates, but is not close enough to the active site to reach short substrates. Cleavage of the modified pepsins with cyanogen bromide identified the methionine nearest the carboxyl terminus of both pepsins as a resiude that remained partially unmodified.

Amino Acids↗