PYRUVATE KINASE ISOZYMES IN NEURONS, GLIA, NEUROBLASTOMA, AND GLIOBLASTOMA

Abstract

Abstract– The distribution of pyruvate kinase isozymes (EC 2.7.1.40) was examined in cells and tissues from the central and peripheral nervous system of the rat. Most tissues contain significant quantities of both the K 4 (fetal type) and M 4 (skeletal muscle type) isozymes plus tetrameric hybrids comprised of various combination of the type M and type K subunits. Retina, for example, contains a five‐mem‐bered hybrid set weighted toward K 4 , while sciatic nerve and spinal cord have patterns very similar to that of adult brain, consisting predominantly of M 4 with small amounts of K 4 and K‐M hybrids. This adult pattern is achieved by a gradual shift from a hybrid set dominated by K 4 in fetal life, to the pattern at birth at which time the two most prominent bands were M 4 and K 2 M 2 , and finally to the adult pattern by about 28 days after birth. Neurons and glial cells were isolated from rat and mouse brains at the various developmental levels. The pyruvate kinase isozyme patterns in the two cell types were similar to each other and to the patterns seen in whole brain homogenates at all ages, indicating similar rates of isozymic maturation in the two cell types. The correlation of maturation with pyruvate kinase isozyme patterns was further tested in cultures of malignant cell lines. A K‐M hybrid set, weighted toward K 4 , was seen in two clonal lines of mouse neuroblastoma under normal culture conditions. However, lowering the serum concentration in the culture medium or adding bromodeoxyuridine caused a shift in the patterns toward type M as the cells differentiated, mimicking in part the in vivo maturation of normal cells. On the other hand, a rapidly growing and poorly differentiated line of rat glioblastoma had only K 4 under all conditions examined.