[Serratia marcescens endonuclease. Properties of the enzyme].

Some physico-chemical properties of endonuclease (EC 3.1.4.9) from Serratia marcescens were studied and the amino acid composition of the enzyme was determined. The protein molecule was shown to contain one SH-group and one S-S-bond, which renders it different from the well studied nuclease (EC 3.1.4.7) from Staph. pyogenes. The conditions for reconstitution of the S-S-bond by dithioerythritol for quantitative estimation of cysteine residues of the endonuclease molecule were selected. The N-terminal amino acid was found to be threonine. The UV spectra for the enzyme are typical for proteins; A 0,1% 1cm,280nm is 1.46, epsilon 25 degrees 280nm,pH7,4 is 47292 M-1 cm-1. The sedimentation coefficient in phosphate buffer sW, 20 degrees is 3.4 S, pI is 6.5 and 7.5.