Purification and properties of two neutral proteinases from Aspergillus nidulans

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 30 900 and 30 000, 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.