Pyruvate kinase isozymes were studied in normal brain tissue (both fetal and adult) and in meningiomas and malignant gliomas. In fetal brain five different forms could be detected by electrophoresis (K4, K3M, K2M2, KM3, and M4). In adult brain the M4-type, K3M hybrid, and K4-type are present; the M isozyme is largely predominant. Alanine inhibition of pyruvate kinase is in agreement with the electrophoretic pattern. Pyruvate kinase from fetal brain and brain of a newborn is more inhibited compared with pyruvate kinase from adult brain. The Lineweaver-Burk plots for pyruvate kinase from fetal brain and brain of the newborn are nonlinear due to the presence of hybrids.
Pyruvate kinase from meningiomas and malignant gliomas is strongly inhibited by alanine. Electrophoresis proved the presence of mainly K4 type and the hybrid K3M, which is in agreement with the alanine inhibition. Determination of the Km's for phosphoenolpyruvate supports this conclusion. The determination of the alanine inhibition of pyruvate kinase may be a diagnostic tool in surgery for gliomas.