SDS and urea are widely used proteinase K activators. Proteinase K becomes more stable when up to 2% SDS or up to 4M urea is added into the reaction when buffers contain these activators. Studies have shown that hydrolysis of albumin by proteinase K was strongly (> 7-fold) stimulated by urea and SDS in a dose-dependent manner. However, with an oligopeptide as a substrate, proteinase K was inactivated by SDS. This suggests that the activation of proteinase K by urea and SDS is caused mainly by denaturation of the protein substrates. It has been shown SDS inhibits ribonuclease activity in the test-tube completely, however it could not prevent RNA degradation during isolation of polysomal RNA due to the reversible characteristics of SDS inhibition. The complete protection, however, was achieved with a combination of SDS and proteinase K. Additionally, the combination of the two activators are effective in degrading “masked” proteins in a poly adenosine phosphoribose experiment which could not be attacked by the proteinase on its own.