On the basis of coincidence of all activation parameters (E, deltaH*, deltaF* and deltaS*) for the reaction of cleavage of cytidine-2';3'-monophosphate catalyzed by "acid" (pH-optimum 4.7) nonspecific RNAses from Aspergillus clavatus and Penicillium brevicompactum (EC 3. 1. 4. 23) it has been proposed that the mechanism of action on this reaction stage (hydrolysis) for both enzymes is equal.