Glycolytic enzymes in the normal human term placenta

The enzymes hexokinase (HK), phosphoglucomutase (PGM), pyruvate kinase (PK) and lactate dehydrogenase (LDH) were assayed in villous tissue homogenates and cell fractions of normal human term placentas. Although lowest in activity and probably rate limiting in glycolysis, hexokinase is theoretically adequate to phosphorylate the total amount of glucose metabolized. PGM and PK activity were in the same range exceeding HK by 10-15 times, suggesting a largely increased breakdown of glycogen-derived glucose in situations of need. Substantially higher LDH activities may reflect the placental ability to utilize lactate from both mother and fetus. Of all enzymes only hexokinase was found to be associated with the particulate matter in considerable amounts.