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  • Title: Purification and characterization of a glucokinase from young tomato (Lycopersicon esculentum L. Mill.) fruit.
    Author: Martinez-Barajas E, Randall DD.
    Journal: Planta; 1998 Aug; 205(4):567-73. PubMed ID: 9684361.
    Abstract:
    In order to clearly establish the properties of the enzymes responsible for hexose phosphorylation we have undertaken the separation and characterization of these enzymes present in tomato fruit (Martinez-Barajas and Randall 1996). This report describes the partial purification and characterization of glucokinase (EC. 2.7.1.1) from young green tomato fruit. The procedure yielded a 360-fold enrichment of glucokinase. Tomato fruit glucokinase is a monomer with a molecular mass of 53 kDa. Glucokinase activity was optimal between pH 7.5 and 8.5, preferred ATP as the phosphate donor (K(m) = 0.223 mM) and exhibited low activity with GTP or UTP. The tomato fruit glucokinase showed highest affinity for glucose (K(m) = 65 microM). Activity observed with glucose was 4-fold greater than with mannose and 50-fold greater than with fructose. The tomato fruit glucokinase was sensitive to product inhibition by ADP (Ki = 36 microM). Little inhibition was observed with glucose 6-phosphate (up to 15 mM) at pH 8.0; however, at pH 7.0 glucokinase activity was inhibited 30-50% by physiological concentrations of glucose 6-phosphate.
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