Main Article Content
Protease of Thermoactinomyces vulgaris was highly thermophilic, as it exhibited its optimal catalytic activity at 65oC, which was much higher than the growth temperature (50oC) of this obligate thermophile. Among the metal ions tested, Mn2+ was most stimulatory, enhancing the specific activity of protease by about 4.4-fold over the control, and broadened the range of its temperature optimum (i.e. 60–65oC). A heavy metal (Hg2+) inhibited the enzyme activity by about 15%. The increase in slope of Arrhenius plot as well as the energy of activation (EA) of T. vulgaris protease due to Mn2+ indicated that this divalent cation enhanced the rate of high-temperature enzyme catalysis at the expense of EA. The increasing concentration of the substrate (casein) increased the specific activity of protease gradually in a dose-dependent manner, both in the absence as well as in the presence (10 mM) of Mn2+. This divalent cation increased the Vmax of this enzyme without affecting Km for the substrate. The thermophilic protease of T. vulgaris appeared to be a metalloenzyme, in which Mn2+ is firmly bound to it, as even 10 mM of EDTA was not able to chelate/remove Mn2+ completely to inhibit its activity.