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Biometals : an international journal on the role of metal ions in biology, biochemistry, and medicine

Action of hexaamminecobalt on the activity of Serratia marcescens nuclease.


PMID 12680708

Abstract

Using CD spectroscopic and kinetic analysis, a refined mechanism of Co(NH3)6(3+) action on activity of Serratia marcescens nuclease was elucidated. The mechanism was identical with previously found mechanisms of Mg2+ and C7H5O2Hg+. Similarly to Mg2+ and C7H5O2Hg+, Co(NH3)6(3+) binding to the DNA substrate induced changes in the secondary structure which resulted in changes of the enzymatic activity of the S. marcescens nuclease. Upon binding of 0.03 Co(NH3)6(3+) per DNA phosphate, highly polymerized DNA displayed A-form characteristics. The DNA transition from B-form to A-form intermediate was followed by a decrease of the nuclease activity. The diminishing nuclease activity was consistent with diminishing values of Km and Kcat. Co(NH3)6(3+) binding to the highly polymerized DNA caused a 1.7-2.8-fold decrease in Km, and 13.3-19.9 decrease in Vmax compared with Mg-DNA complex. A vast excess of Co(NH3)6(3+) did not affect the activity of S. marcescens nuclease if the DNA in the assay mixture remained in its B-form conformation. Preincubation of S. marcescens nuclease with Co(NH3)6(3+) did not influence the tertiary structure of the enzyme.