Identification of human red cell glutamate-pyruvate transaminase (GPT) phenotypes by isoelectric focusing

Isoenzymes of human red cell glutamate-pyruvate transaminase (GPT) were resolved by isoelectric focusing (IEF) of hemolysates in polyacrylamide gels at pH 5.0-7.0. The bands of enzyme activity required both alpha-ketoglutarate and L-alanine in the staining mixture for visualization, indicating that the bands were not lactate dehydrogenase or glutamate dehydrogenase. Phenotyping of 41 individuals by IEF, including types GPT 1, 2A, 1-2A, 1-2B, and 2A-2B, agreed with the typing results obtained by electrophoresis in starch gels and in polyacrylamide gels at acid and alkaline pH. Analysis of one kindred demonstrated autosomal codominant transmission of the rare GPT*2B gene through 3 generations. IEF facilitates phenotyping by permitting identification of the GPT types on a single gel with a considerable reduction in time and cost. Although no new variants were found in this investigation, IEF may be more powerful for the recognition of presently undetected variants of GPT.