High and low molecular weight proteolytic activities in prawn (Metapenaeus brevicornis) muscle.

Muscle extract of prawn (Metapenaeus brevicornis) expressed high azocoll lytic activity compared to extracts of many other prawn varieties; the activity was also inhibited to a small extent by dithiothreitol. Ammonium sulphate precipitation, subsequent extraction at pH 5.6 and chromatography revealed the occurrence of two types of azocoll lytic activities: one, high molecular weight (630 kDa) and the other low molecular weight (< 30 kDa) enzyme. The former was stimulated by dithiothreitol whereas the latter was inhibited. SDS PAGE of high molecular weight preparation did not show homogeneity but the profile was similar to that of the low molecular weight fraction. Gel filtration of high molecular weight enzyme following incubation at high pH revealed the formation of low molecular weight fractions having activity towards azocoll. Chymotrypsin-like activity associated with high molecular weight enzyme was also susceptible to dissociation by high pH. Azocoll lytic activity of both enzymes was strongly inhibited by 1,10-phenanthroline.

Aminopeptidase from the skeletal muscle of fresh water fish Tilapia mossambica.

An aminopeptidase from the skeletal muscle of fish, Tilapia mossambica, was partially purified to 96-fold using salt precipitation, ion-exchange chromatography and molecular sieve chromatography. The enzyme showed optimum activity between pH 6.5-7.5 at 43 degrees C and Vmax and Km of 14.36 units/mg and 0.059 mM respectively with alanine beta-naphthylamide as the substrate. The aminopeptidase having a molecular weight of 305 kDa was activated by sulphydryl compounds and Co2+ and inhibited by bestatin, puromycin and metal chelators. Inhibition caused by metal chelators could be reversed by the addition of Co2+. Inclusion of L-amino acids, particularly isoleucine and leucine, in the assay medium caused inhibition of the enzyme activity. Substrate specificity together with inhibition and activation pattern indicated that the enzyme is alanine aminopeptidase.