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Distribution of adenosine 5'-triphosphate (ATP)-dependent hexose kinases in microorganisms
Abstract:
A systematic study of adenosine triphosphate (ATP)-dependent hexose kinases among microorganisms has been undertaken. Sixteen hexose kinases of five major types were partially purified from 12 microorganisms and characterized with respect to specificity for sugar and nucleotide substrates and Michaelis constants for the sugar substrates. Glucokinase activities that phosphorylate glucose and glucosamine are inhibited by N-acetyl-glucosamine and xylose, were found to be present in the non-sulphur photosynthetic bacteria Rhodospirillum rubrum, the blue-green algae Anacystis montana, and the protists Chlorella pyrenoidosa and Chlamydomonas reinhardtii (green algae), Hypochytrium catenoides (Hypochytridiomycete) and Saprolegnia Iitoralis (Oomycete). The myxobacteria Stigmatella aurantiaca contains a glucokinase activity with a different specificity pattern. Anacystis and Chlorella, besides their glucokinase activities, contain highly specific fructokinases, although that from Anacystis can also phosphorylate fructosamine; fructokinase from Anacystis has a molecular weight of 20 000, and exhibits a sigmoidal saturation curve for ATP when the Mg2+/ATP ratio is 2; this curve is transformed to a Michaelian one when under the same conditions an excess of Mg2+ (5 mM) is added. Saprolegnia however, besides the glucokinase, contains a mannofructokinase activity that phosphorylates mannose (Km 0.06 mM) and fructose (1 mM). On the other hand, hexokinase, a low specificity enzyme, was detected in the protist Allomyces arbuscula (Chytridiomycete) and in fungi Mucor hiemalis and Phycomyces blakesleeanus (Zygomycetes), and Schizophyllum commune (Basidiomycete). Schizophyllum contains a glucomannokinase activity together with hexokinase activity. The pattern of distribution of ATP-dependent hexose kinases among microorganisms seems to parallel that reported for biosynthetic pathways for lysine. The correlation with other biochemical parameters is also considered.