A mutant strain of Escherichia coli requiring lipoic acid for normal growth

Abstract

PROCEEDINGS OF THE BIOCHEMICAL SOCIETY sperm extracts consistently gives two distinct peaks of enzyme activity. One peak is eluted at a position corresponding to a molecular weight of 100000, whereas the other peak is eluted at the void volume from Sephadex G-150 (mol.wt. > 500000). No significant change from one peak to the other was observed when either form was rerun separately on Sephadex, even when run in the presence of high salt concentrations (0-75M). No difference in the Km of fructose or glucose could be detected between the two forms of hexokinase. Horizontal starch-gel electrophoresis separates hexokinase into three bands. One of these migrates very slowly from the origin and is characteristic of sperm hexokinases. Katzen (1967) discovered this slowly migrating form of hexokinase in testis and epididymal extracts and deduced that it resulted from the sperm in these tissues. Separate electrophoresis of each of the two peaks from gel filtration strongly suggests that this 'sperm-type' hexokinase band on electrophoresis is identical with the highermolecular-weight enzyme peak from gel filtration. The low mobility of the 'sperm-type' band may well be due to its being a relatively large molecule, retarded by the sieving action of starch gel, rather than to its charge or chemical properties. This work is supported by a grant from the Pig Industry Development Authority.