[Nuclease isoforms of natural and recombinant strains of Serratia marcescens. Comparative characteristics of plasma desorption mass spectrometry].

The primary structure of isoforms of natural nuclease secreted by Serratia marcescens as well as of recombinant nuclease produced by Escherichia coli has been characterized by plasma desorption mass spectrometry. The isoforms were isolated from the purified nuclease on a DEAE-cellulose anion-exchange column and digested with endoproteinase Lys-C. The peptides generated were isolated by reversed phase IIPLC and their molecular masses determined by plasma desorption mass spectrometry. Among the nuclease isoforms secreted by parent cells, a new isoform, Sm3, was found. Comparison of the peptides yielded by nuclease Sm2 and two isoenzymes, Sm1 and Sm3, demonstrated their distinction only in the N-termini; three amino acids are lacking in Sm1 and one residue in Sm3. Identity was demonstrated between nucleases Sm1 and Sm2 produced by S. marcescens and the isoforms rSm1 and rSm2 secreted by the recombinant E. coli strain.