Lactoferrin Is the Major Deoxyribonuclease of Human Milk

S. E. Babina^1,2, T. G. Kanyshkova¹, V. N. Buneva¹, and G. A. Nevinsky^1*

¹Novosibirsk Institute of Bioorganic Chemistry, Siberian Division of the Russian Academy of Sciences, pr. Lavrentieva 8, Novosibirsk 630090, Russia; fax: (3832) 33-3677; E-mail: nevinsky@niboch.nsc.ru

²Novosibirsk State University, ul. Pirogova 4, Novosibirsk 630090, Russia

^* To whom correspondence should be addressed.

Received September 3, 2003; Revision received February 18, 2004

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Lactoferrin is the major iron-transferring protein of human barrier fluids such as blood and milk. It is a polyfunctional protein capable of binding DNA exposed on the surface of various cells. Electrophoretically homogenous lactoferrin was prepared by sequential chromatography of human milk proteins on DEAE-cellulose, heparin-Sepharose, and Sepharose containing immobilized anti-lactoferrin antibodies. By subsequent chromatography on Blue Sepharose the resulting lactoferrin was fractionated into several subfractions with different affinity for the sorbent, and this was associated with separation of additional lactoferrin peaks with DNase activity from the main peak. By various techniques, in particular, by in situ testing the DNase activity of lactoferrin in a DNA-containing gel after SDS-electrophoresis, hydrolysis of DNA was for the first time shown to be an intrinsic property of lactoferrin. The substrate specificity of lactoferrin in hydrolysis of DNA was different from specificities of known human DNases. Hydrolysis of DNA was activated by bivalent metal ions and also by ATP and NAD. Unlike the main fraction of lactoferrin with the highest affinity for Blue Sepharose, all protein subfractions with DNase activity were cytotoxic and suppressed growth of human and mouse tumor cell lines.

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KEY WORDS: lactoferrin, human milk, hydrolysis of DNA, allosteric effect

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