The M1 and M2 subunits of rat pyruvate kinase are encoded by different messenger RNAs.

The question of whether the M1- and M2-type isozymes of pyruvate kinase are synthesized by a common mRNA was examined by isolating total RNA from rat skeletal muscle and AH-130 Yoshida ascites hepatoma cells, which express the M1- and M2-type isozymes, respectively, and translating the preparations in a rabbit reticulocyte lysate system. The newly synthesized pyruvate kinase subunits were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing under the denaturing condition. The pyruvate kinase subunit synthesized from hepatoma cell RNA had a slightly larger molecular weight and higher pI value than the subunit from muscle RNA. When a mixture of the two RNAs was added to the lysate, the same result was obtained. Thus, it is concluded that the M1- and M2-type isozymes are translated from different messenger RNAs.