The main goal of the investigation was to analyze the mechanism of Mg2+ action on the digestive activity of Serratia marcescens nuclease towards RNA due to the potential application of the nuclease as a reagent for removing nucleic acids from biomedical samples as well as an antiviral factor. Examination of the mechanism revealed that it was similar to the mechanism of the metals actions on the DNase activity. The optimal Mg2+ amount was linked with the changing secondary structure of RNA—substrates within A-helix. Addition of Mg2+ was found to affect both the rates of products dissociations from the enzyme-substrate complexes and the enzyme associations with the substrates, that was supported by strong increase in the Kcat values and change in the Km values. Comparing the mechanisms of Mg2+ action on RNase and DNase activities in S. marcescens nuclease, we identified a preference for DNA in the absence of Mg2+ that was supported with the Kcat values.

Examination of the effects of mononucleotides on Sma nuc endonuclease originated from Gram negative bacterium Serratia marcescens displayed that any mononucleotide produced by Sma nuc during hydrolysis of DNA or RNA may regulate the enzyme activity affecting the RNase activity without pronounced influence on the activity towards DNA. The type of carbohydrate residue in mononucleotides does not affect the regulation. In contrast, the effects depend on the type of bases in nucleotides. AMP or dAMP was classified as a competitive inhibitor of partial type. GMP, UMP, and CMP were found to be uncompetitive inhibitors that suggest a specific site(s) for the nucleotide(s) binding in Sma nuc endonuclease.