Of 14 actinomycete isolates in our collection from various biotopes in Manipur that were screened
on skim milk agar, 5 strains produced high amounts of extracellular proteases as indicated by large halos. One
isolate HA-4, obtained from limestone quarry sample, was selected for further studies. The selected isolate was
subjected to polyphasic characterization and identified as Nocardiopsis prasina HA-4. The organism grew well
at temperatures of 20-42°C, pH 7-10 and in presence of 2-10% NaCl (with more growth at 10% salt). Cultural and
environmental conditions for protease production by HA-4 were studied. Sucrose (5%,w/v) and peptone (0.2%,
w/v) were found to be the best C and N sources for protease production respectively. The optimum temperature
for the enzyme from HA-4 was 55°C and it had two pH optima at 7.0 and 10.0. Ca2+ and Mg2+ partially inhibited
enzyme activity whereas Hg2+ completely inhibited it. Interestingly Fe2+ was found to have stimulatory effect,
which has been rarely reported. The wide tolerance of temperature and pH by Nocardiopsis prasina HA-4
protease makes it an ideal candidate to be investigated further for potential application as a detergent additive.