Aminopeptidases of Physarum polycephalum during growth and differentiation

A soluble cell fraction from exponentially growing microplasmodia of the slime mold, Physarum polycephalum, contains 12 electrophoretically distinguishable enzymes capable of hydrolyzing the aminopeptidase substrate, l-leucyl-2-naphthylamide (LNA) at pH 6.5. These enzymes appear to represent three distinct groups of LNA isoenzymes on the basis of electrophoretic mobilities, substrate ranges, and effects of divalent cations and of EDTA on peptidase activity. When spherulation is induced by transfer of microplasmodia to a starvation medium, there is a brief increase in one form of one of the enzymes followed by complete abolition of that enzyme group. These changes in the enzymatic profile occur within 4–5 h of transfer to a starvation medium, though spherules do not appear until 15–20 h later.