Purification and Properties of Two Neutral Proteinases from Aspergillus nidulans

SUMMARY: Two proteinases have been purified from mycelial extracts of Aspergillus nidulans. Both enzymes have pH optima between 6.5 and 7.5 and are inhibited by phenylmethane sulphonyl fluoride and by di-isopropyl fluorophosphate. The molecular weights and isoelectric points of proteinase I and proteinase II are 30900 and 30000, and 4.6 and 4.3, respectively. Both enzymes have a similar range of substrate specificities. The principal differences in their properties are that proteinase I is sensitive to inhibition by 1 mM mercurials whereas proteinase II is not appreciably inhibited at this concentration, and that proteinase I is much more sensitive to denaturation by urea, guanidine hydrochloride and sodium dodecyl sulphate.