Isoforms of Serratia marcescens Nuclease. The Role of Mg²⁺ in the Hydrolysis Mechanism

M. N. Filimonova,^1,2 V. P. Gubskaya,³ I. A. Nuretdinov,³ M. J. Benedik,⁴ L. M. Bogomol’naya,¹ M. A. Andreeva,¹ and I. B. Leshchinskaya¹

¹Department of Microbiology, Kazan State University, ul. Lenina 18, Kazan, 420008 Russia; fax: (843-2) 380-994; E-mail: maria.filimonova@ksu.ru

²To whom correspondence should be addressed.

³Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences, ul. Arbuzova 8, Kazan, 420088 Russia; fax: (843-2) 752-253; E-mail: IN@glass.ksu.ras.ru

⁴Department of Biochemical and Biophysical Sciences, University of Houston, Houston, TX 77204-5934, USA; fax: (713) 743-8351; E-mail: benedik@uh.edu

Submitted February 7, 1997; revision submitted April 18, 1997.

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Structural and functional differences between isoforms Sm1 and Sm2, a lack of influence of free Mg²⁺ on the isoform structures, formation of DNA--magnesium complex serving with great probability as a real substrate for the nuclease has been summarized on the basis of experimental data. Mg²⁺ forming a complex with phosphate groups of DNA are supposed to further increase theelectrophilicity of the phosphorus atoms besides causing a conformational change of the substrate.

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KEY WORDS: nuclease, Serratia marcescens, isoforms, Mg²⁺, Na--DNA, Mg--DNA, CD.

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