Abstract
Proteinase A was purified by an improved large scale procedure and split into fragments by means of trypsin, cyanogen bromide, hydroxylamine, and o-iodosobenzoic acid. On the basis of high degrees of homology with cathepsin D and pepsin its amino acid sequence was determined. Proteinase. A contains 329 amino acid residues, and in addition 8.5% neutral sugar and 1% glucosamine, attached to asparagines in positions 67 and 267. Proteinase A contains two disulfide bonds, as opposed to three in mammalian aspartic proteinases. Comparison with the tertiary structure of pepsin indicates, that the two catalytically essential aspartic acid residues, and the residues corresponding to their surroundings, are conserved. The sequence shows 46% identity with porcine cathepsin D and 40% with porcine pepsin. An aspartic proteinase from Saccharomyces carlsbergensis had the same N-terminal 40 amino acid sequence as proteinase A. Immunological cross-reactivity between proteinase A and calf chymosin was demonstrated by immune blotting assay.
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