Occurrence of two distinct molecular species of cathepsin B in carp Cyprinus carpio

ABSTRACT:   We purified cathepsins B₁ and B₂ from the ordinary muscle of carp Cyprinus carpio . The N-terminal amino acid sequences (12 residues) of 29 kDa bands of cathepsins B₁ and B₂ are the same and showed high homology of 75% and 83%, respectively, with the heavy chain of rat and human cathepsins B. Based on conserved sequences of other cathepsins B and the N-terminal amino acid sequences of 29 kDa bands, we cloned carp cathepsin B cDNA. The nucleotide sequence of carp cathepsin B cDNA consists of 1470 bp including a 993 bp open reading frame, encoding a deduced protein of 330 amino acids. The deduced amino acid sequence of carp cathepsin B has similarity of 80% to rainbow trout cathepsin B and of 76–78% to other vertebrate cathepsins B. The sequence of its isoform was also determined during molecular cloning, which has 94.8% similarity with first cloned cathepsin B. They are completely same in N-terminal amino acid sequence of heavy chain, active site and potential N-glycosylation site. This indicates there are at least two kinds of cathepsin B functioning in vivo in carp.