Chymotrypsinogen amino acid composition

Table I gives the amino acid composition of bovine chymotrypsinogen A. Quite similar results for most amino acids have been obtained for this protein in two laboratories by the usual chromatographic technique in its manual or automatic (83) form involving all the necessary corrections and extrapolations to zero time. Cystine has been determined as cysteic acid after pcrformic acid oxidation. Values of tryptophan are probably less satisfactory sin( e they are derived from spectrophotometric or microbiological determinations. The protein contains only 2 histidines, 2 methionines, 4 arginines, 4 tyrosines, and 5 cystines per mole.

As in bovine chymotrypsinogens A and B, the single NH2-terniinal residue in porcine chymotrypsinogen A is half-cystine. The amino acid composition and the molecular weight of the protein are given in Table I. 

Hydrolysis of peptides or proteins with acid yields a mixture of free a-amino acids. When completely hydrolyzed, each type of protein yields a characteristic proportion or mixture of the different amino acids. The 20 common amino acids almost never occur in equal amounts in a protein. Some amino acids may occur only once or not at all in a given type of protein others may occur in large numbers. Table 3-3 shows the composition of the amino acid mixtures obtained on complete hydrolysis of bovine cytochrome c and chymotrypsinogen, the inactive precursor of the digestive enzyme chymotrypsin. These two proteins, with very different functions, also differ significantly in the relative numbers of each kind of amino acid they contain. 

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