Stimulation of proteinase K action by denaturing agents: application to the isolation of nucleic acids and the degradation of 'masked' proteins.

Hydrolysis of serum albumin by proteinase K was strongly (greater than 7-fold) stimulated by urea and dodecylsulfate in a dose-dependent manner. With an oligopeptide as substrate, however, proteinase K was inactivated by dodecylsulfate. This indicates that the apparent activation of proteinase K by urea and dodecylsulfate is caused primarily by denaturation of the protein substrates. Although dodecylsulfate inhibited ribonuclease activity in the test-tube completely, it could not prevent RNA degradation during isolation of polysomal RNA, to which ribonuclease had been added, because of the reversible nature of the dodecylsulfate inhibition. Complete protection of RNA, however, was achieved by a combination of dodecylsulfate and proteinase K. The combined action of the detergent and proteinase K was also effective in degrading "masked" proteins in a poly(adenosine diphosphoribose) preparation which could not be attacked by the proteinase alone.