Distinctive catalytic actions of carp dipeptidases from ordinary muscle and intestine

Although carp muscular and intestinal dipeptidases are metalloenzymes acting only on dipeptides, some structural and enzymatic differences occur between them. The present study verifies distinctive actions during dipeptide hydrolysis by these enzymes in terms of their kinetic characterization. The intestinal enzyme was differentially inhibited by EDTA and 1,10-phenanthroline, whereas these compounds induced a similar level inhibition of the muscular enzyme. The Km and Vmax values of both enzymes for l-leucine-glycine hydrolysis varied during incubations with 1,10-phenanthroline and EDTA, and the Km or Vmax values of the intestinal enzyme increased or remained the same with increasing concentrations of 1,10-phenanthroline, respectively. Analysis of the kinetic parameters indicated that Co2+ and Mn2+ had noncompetitive effects on the muscular enzyme and that a noncompetitive activation on the intestinal enzyme was stimulated by 1.5 mM of Mg2+ and with increasing concentrations of Mn2+. The muscular enzyme acted on a wide range of l-configuration dipeptides, whereas the intestinal enzyme acted only on a select range of dipeptides with a hydrophobic amino acid at the N-terminal position. The Kcat/Km values of both enzymes for dipeptide hydrolysis showed that highly hydrophobic dipeptides served as their preferential substrates. Other kinetic parameters demonstrated distinctive hydrolytic action of the two enzymes on these dipeptides: a strong affinity of the low catalytic rate muscular enzyme, and a weak affinity of the high catalytic rate intestinal enzyme.