A Hybrid Mutant Form of Escherichia coli Inorganic Pyrophosphatase

I. S. Velichko¹ and A. A. Baykov^1,2

¹Belozersky Institute of Physico-Chemical Biology and School of Chemistry, Lomonosov Moscow State University, Moscow 119899, Russia; fax: (7-095) 939-31-81; E-mail: abaykov@protchem.genebee.msu.su

²To whom correspondence should be addressed.

Submitted November 5, 1996.

The inorganic pyrophosphatase of Escherichia coli is a tight hexamer of identical subunits. Upon interaction of its two mutant forms in which the trimer--trimer contacts are weakened because of E20D and H136Q substitutions, a hybrid hexameric E20D/H136Q-PPase is formed. The catalytic activity of its constituent H136Q trimer is same as of its hexamer, whereas metal-binding affinity is significantly decreased. These results point to an interdependence of two trimers in catalysis by hexameric pyrophosphatase.

KEY WORDS: pyrophosphatase, quaternary structure, site-directed mutagenesis.

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