Induction of glycolytic enzyme synthesis in proliferating fibroblasts. Study of phosphofructokinase, glucose phosphate isomerase and pyruvate kinase.

Specific activity of phosphofructokinase is 7-8-fold higher in exponentially growing human fibroblasts than in quiescent cells, but the difference is considerably less pronounced for two other glycolytic enzymes, glucose phosphate isomerase and pyruvate kinase. The ratio of the F-type to L-type phosphofructokinase subunits is essentially the same in growing and resting cells, 4:1. F-type-phosphofructokinase-related antigen concentration is decreased in resting cells as compared with proliferating fibroblasts, but relatively less than the enzyme activity; the ratio of the enzyme activity to the antigen concentration (immunological specific activity) is therefore lower in resting than in growing fibroblasts. Synthesis of phosphofructokinase, as a percentage of the total protein synthesis, is about 30-fold greater during the proliferative phase than in quiescent cells, but this difference is only 3-4-fold for glucose phosphate isomerase and pyruvate kinase. Modulation of the synthesis of phosphofructokinase therefore seems to be responsible for the changes of its specific activity in function of cell proliferation. The appearance of some inactive cross-reacting material in quiescent cells is probably due to post-translational alteration of the pre-synthesized molecules. Compared with other glycolytic enzymes, such as glucose phosphate isomerase and pyruvate kinase, phosphofructokinase seems to be the (or one of the) preferential target of glycolytic induction in proliferating cells.