Pyruvate Kinase Isozymes from Rat Tissues

Developmental and aging patterns of pyruvate kinase (PK) isozymes (PK 1, PK 2, PK 3, and PK 4) from rat liver, kidney, heart, and skeletal muscle were studied by electrophoretic, chromatographic and immunochemical techniques. During the first 2 weeks of postnatal life a decline of total PK activity occurred in liver, kidney, and heart followed by an increase to adult or higher than adult levels after weaning. Skeletal muscle PK increased steadily from very low levels before birth to steady state levels by the end of the 2nd month. It was demonstrated that changes in enzyme activity during development were the result of changes in the amount of enzyme protein. Both PK isozymes from rat liver (PK 1 and PK 4) decreased during the first 2 weeks of postnatal life. Liver PK 1 sharply increased after weaning, whereas liver PK 4 remained at the level of 3 to 10% of the total enzymatic activity. PK 4, the only isozyme detected in fetal rat kidney, predominated throughout development, although PK 1, PK 2, and PK 3 appeared shortly after birth. A shift of PK 4 to PK 3 occurred in both cardiac and skeletal muscle with passage from the fetal to the neonatal stage of development. Adult skeletal muscle contains only PK 3, which is also the predominant form in cardiac muscle. Antiserum prepared against purified PK 3 from skeletal muscle neutralized PK 2, PK 3, and PK 4 from kidney but did not cross-react with liver and kidney PK 1. Developmental changes in total PK activity and in PK isozyme patterns in rat liver and kidney are discussed in terms of their possible significance in the regulation of gluconeogenesis.