Liver Cell Heterogeneity. The Distribution of Pyruvate Kinase and Phosphoenolpyruvate Carboxykinase (GTP) in the Liver Lobule of Fed and Starved Rats

Abstract

Pyruvate kinase [EC 2.7.1.40] and phosphoenolypyruvate carboxykinase [EC 4.1.1.32] activites were determined in microdissected freeze-dried liver cells from the periportal and pericentral area of the liver lobule. Pyruvate kinase activity was measured by a microfluorimetric procedure adapted to 20-200 ng tissue dry wt. In livers from fed rats, its activity was twice as high in the central zone as in the periportal cells; starvation reduced this gradient by decreasing central activities. Phosphoenolypyruvate carboxykinase activity was measured by a microradiochemical technique in 100-300 ng tissue dry wt. In livers from fed rats, this enzyme was nearly 3 times more active in the periportal cells than in the central area. Starvation increased this enzyme in both zones with a more pronounced change in the central cells. A heterogeneous distribution of enzymes of carbohydrate metabolism in the liver lobule was indicated. Gluconeogenesis seems to be localized preferentially in periportal hepatocytes; the glycolytic enzyme was more active in cells surrounding the pericentral liver cells.