| Abstrakt: |
The purification is described of rat hepatic hexokinase type III and kidney hexokinase type I on a large scale by using a combination of conventional and affinity techniques similar to those previously used for the purification of rat hepatic glucokinase [Holroyde, Allen, Storer, Warsy, Chesher, Trayer, Cornish-Bowden & Walker (1976) Biochem. J. 153, 363-373] and muscle hexokinase type II [Holroyde & Trayer (1976) FEBS Lett. 62, 215-219]. The key to each purification was the use of a Sepharose-N-aminoacylglucosamine affinity matrix in which a high degree of specificity for a particular hexokinase isoenzyme could be introduced by either varying the length of the aminoacyl spacer and/or varying the ligand concentration coupled to the gel. This was predicted from a study of the free solution kinetic properties of the various N-aminoacylglucosamine derivatives used (N-aminopropionyl, N-aminobutyryl, N-aminohexanoyl and N-aminooctanoyl), synthesized as described by Holroyde, Chesher, Trayer & Walker [(1976) Biochem. J. 153, 351-361]. All derivatives were competitive inhibitors, with respect to glucose, of the hexokinase reaction, and there was a direct correlation between the Ki for a particular derivative and its ability to act as an affinity matrix when immobilized to CNBr-activated Sepharose 4B. Muscle hexokinase type II could be chromatographed on the Sepharose conjugates of all four N-aminoacylglucosamine derivatives, although the N-aminohexanoylglucosamine derivative proved best. This same derivative was readily able to bind hepatic glucokinase and hexokinase type III, but Sepharose-N-amino-octanoyl-glucosamine was better for these enzymes and was the only derivative capable of binding kidney hexokinase type I efficiently. Separate studies with yeast hexokinase showed that again only the Sepharose-N-amino-octanoylglucosamine was capable of acting as an efficient affinity matrix for this enzyme. Implications of these studies in our understanding of affinity-chromatography operation are discussed. |
