Isozymes of Human Red Cell Glucose‐6‐phosphate Dehydrogenase*

Summary With most gel electrophoretic techniques used for genetic studies of human G‐6‐PD, the activity from hemolysates of males migrates predominantly as a single band. Under two conditions of starch gel electrophoresis, however, dual bands of red cell G‐6‐PD may be seen. These exceptions are: (a) two prominent bands of G‐6‐PD that appear after starch‐gel electrophoresis in a discontinuous‐borate buffer system, and (b) a minor band of red cell G‐6‐PD that moves about 80 percent as fast as the major band in a number of buffer and gel systems. The faster band of (a) was found to be absent or less prominent in samples that had been incubated under conditions previously shown to cause aggregation of G‐6‐PD subunits. Electrophoresis in starch gel of various concentrations revealed that the slower component of (a) is of larger molecular size than the faster component. In contrast, the minor component of (b) was found to be similar in molecular size to the major component. The isolated minor component had the electrophoretic mobility of the major band after treatment with β‐mercaptoethanol. Reappearance of a minor band was obtained by incubation of major band G‐6‐PD with another protein fraction from normal red cells, in the absence of β‐mercaptoethanol. It is proposed that bands of (a) represent simply the aggregated and disaggregated form of G‐6‐PD. The minor band of (b) appears to be a complex of a subunit of G‐6‐PD and another protein.