THE 50-KDA GLUCOSE 6-PHOSPHATE-SENSITIVE HEXOKINASE OF SCHISTOSOMA-MANSONI

Hexokinase has been purified from adult Schistosoma mansoni worms and the activity shown to be associated with a single protein species havi ng an M(r) about 50,000. This protein is recognized on Western blots p robed with antisera against rat Type I hexokinase or against a recombi nant S. mansoni hexokinase that had been expressed in Escherichia coli using a previously cloned cDNA. An 18-residue N-terminal sequence det ermined for the purified S. mansoni hexokinase is identical to that de duced from the nucleotide sequence of the cDNA, consistent with the vi ew that the cloned cDNA encodes the hexokinase characterized in the pr esent study. The S. mansoni enzyme has a relatively low K-m (approxima te to 60 mu M) for glucose and is sensitive to inhibition (competitive versus ATP, K-i approximate to 50 mu M) by its product, glucose 6-pho sphate (Glc-6-P). With these kinetic properties and 50 kDa molecular m ass, S. mansoni hexokinase resembles the ancestral hexokinase predicte d to have given rise, by gene duplication and fusion, to the present d ay 100-kDa Glc-6-P-sensitive mammalian hexokinases. The schistosomal h exokinase represents the first 50-kDa Glc-6-P-sensitive hexokinase who se sequence has been obtained. The schistosomal hexokinase does not bi nd to mitochondria, consistent with its lack of a hydrophobic segment at the N terminus which is required for binding of the mammalian Type I and II isoenzymes to mitochondria. The marked Crabtree effect exhibi ted by S. mansoni cercariae may be at least partly attributed to the e xpression of rather high levels of a hexokinase having a high affinity for glucose but only a moderate sensitivity to product inhibition by Glc-6-P.