Neutral Proteinase of Carp Muscle

A neutral proteinase has been extracted from carp muscle and partially purified. The enzyme is a typical neutral proteinase maximally active at pH 7.2 and at 40°C: it hydrolyzed hemoglobin but neither casein nor albumin. The activity was inhibited by both EDTA and o‐phenanthroline, but not by diisopropylphosphorofluoridate. SH‐compounds such as sodium thioglycollate and dithiothreitol, and Ca ++ did not increase the activity. The proteinase liberated tri‐ or tetra‐peptides from hemoglobin and acted well on the hydrolysates of hemoglobin produced by the carp muscle cathepsin D. The enzyme is a new neutral endopeptidase (tentatively called subendopeptidase) not previously reported in fish muscle.