Biochemical evidence that Escherichia coli hyi (orf b0508, gip) gene encodes hydroxypyruvate isomerase

We found a significant activity of hydroxypyruvate isomerase in Escherichia coli clone cells harboring an E. coli gene (called orf b0508 or gip), whic h is located downstream of the glyoxylate carboligase gene. We newly design ated the gene hyi. The enzyme was purified from cell extracts of the E. col i clone. The enzyme had a molecular mass of 58 kDa and was composed of two identical subunits. The optimum pH for the isomerization of hydroxypyruvate was 6.8-7.2. The enzyme required no cofactor. It exclusively catalyzed the isomerization between hydroxypyruvate and tartronate semialdehyde. The app arent K-m value for hydroxypyruvate was 12.5 mM. The amino acid sequence of E. coli hydroxypyruvate isomerase is highly similar to those of glyoxylate -induced proteins, Gip, found widely from prokaryotes to eukaryotes. (C) 19 99 Elsevier Science B.V. All rights reserved.