Identification and kinetic studies of an inducible mannokinase from a Streptomyces strain

Crude extracts from cells of a Streptomyces strain isolated from a palm-grove soil and grown on different carbon sources showed a constitutive glucokinase. Specifically inducible kinase activity for mannose was found in cells grown on mannose or beta-D-mannan. The activity on mannose was due to a highly specific mannokinase (ATP:D-mannose 6-phosphotransferase, EC 2.7.1.7) which has been separated from the glucokinase by Ultrogel AcA 54 gel filtration chromatography. Initial velocity and inhibition product studies were carried out to investigate the reaction pathway. In the absence of products, reciprocal plots intersecting on the abscissas were observed when either mannose or ATP concentration was varied in the presence of several fixed concentrations of the non-varied substrate. Km values for mannose and Mg-ATP complex are 0.33 and 1.1 mM, respectively. In the product inhibition studies, mannose-6-P was observed to be competitive with mannose and non-competitive with Mg-ATP. The reverse was observed when ADP was used as inhibitor. These data are consistent with a random sequential Bi-Bi mechanism with two dead-end ternary complexes.