Some properties of a zinc-dependent hexokinase from Neurospora crassa

Abstract

A hexokinase which phosphorylates glucose and, at a lower rate, mannose, fructose and glucosamine was purified 60-fold from N. crassa, Wild Type (146). The phosphorylation product from glucose is shown by chromatographic and enzymlc methods to be glucose 6-phosphate. The enzyme is competitively inhibited by N-acetylglucosamlne. The enzyme is inhibited by sodium ethylene-diaminetetra-acetate, iodoacetate and p-chloromercuribenzoate. The inhibition by the last compound is reversed by reduced glutathione. Zinc deficiency in the mycelial felts reduced hexokinase activity. The enzyme activity was brought up to 90% of the control mats within 12 hours after adding Zn2+ ions to the zinc-deficient culture medium. The enzyme prepared from zinc-deficient felts was activated to about 30% of the normal activity, by adding Zn2+ ions to it in vitro, but not zinc ethylenediaminetetra-acetate. Zinc sulphate gave some protection to the SH groups in the enzyme from inhibition by p-chloromercuribenzoate, but the metal did not reverse the inhibitory effect if added after the inhibition. The possible role of zinc in hexokinase action is discussed.