Isolation of four components from purified human erythrocyte hypoxanthine-guanine phosphoribosyltransferase by isoelectric focusing.

Erythrocyte HGPRT from a male donor was partially purified by DEAE-cellulose chromatography and by fractionation between 35 and 65% ethanol. Isoelectric focusing of the ethanol fraction resolved HGPRT activity into four components which were numbered I-IV beginning with the one nearest the cathode. A second isoelectric focusing of component II (the most active) resulted in 94% of the activity as a single component. When mixed, however, the four components could be separated again by isoelectric focusing. The appearance of these different molecular forms of the enzyme could be due to post-transcriptional alterations or to formation of enzyme complexes.