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The digest of penicillopepsin (EC 3.4.23.7) with protease II from Myxobacter AL-1 gave five fragments which were separated on a Biogel P-100 column in 70% formic acid. The fragments were from 16 to 125 amino acids long. Two fragments were also isolated from a digest with a protease from Staphylococcus aureus. The analysis of these fragments by automatic sequencer gave a number of overlaps of the chymotryptic and thermolytic peptides. The available amino acid sequence data for penicillopepsin described in this paper and the accompanying papers (Kurosky, A. and Hofmann, T.:Can. J. Biochem. 54, 872 (1976);Rao, L and Hofmann, T.:Can. J. Biochem.54,885 (1976); Harris, C.I.,Rao, L., Shutsa, P., Kurosky, A. and Hofmann, T.: Can. J. Biochem. 54,895 (1976) have been combined and yield 15 fragments which range in lengths from 3 to 112 amino acid residues. These unique fragments account for virtually all the amino acids of the fungal protease. Four of the fragments with a total of 194 residues (about 60% of the molecule) have been aligned with corresponding sections of pig pepsin (EC 3.4.23.1) and with part of the N-terminal sequence available for calf chymosin (EC 3.4.23.4). In the alignments about 37% of the residues in the fungal enzyme are identical with at least one of the mammalian enzymes. An additional 20% are chemically similar. These results, together with previously reported active site directed modifications, show conclusively that penicillopepsin is an evolutionary homologue of the mammalian acid proteases.

The amino acid sequence of peptides isolated from a tryptic digest of penicillopepsin (EC 3.4.23.7), a subtilisin (EC 3.4.21.14) digest of maleylated penicillopepsin, and a chymotryptic digest of penicillopepsin modified with dinitrophenylsulfenyl (DNPS) chloride have been determined. The first two digests identified four of the five lysyl residues of the enzyme as well as the N-terminal peptide. The third digest provided overlaps at three of the tryptophanyl residues. The DNPS-tryptophan peptides were isolated on an affinity column prepared by coupling dinitrophenyl antibody raised in sheep to cyanogen bromide-activated Sepharose.