Glycolytic Enzymes in the Normal Human Term Placenta

Abstract

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 glycogenderived 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.

Effect of Perfusion on the Biochemical Composition of the Human Placenta

“…No study is known to us in which the attempt is made to measure the blood content of the analyzed tissue samples and to correlate biochemical data to this con taminating component. In an earlier study on placental glycolytic enzymes we found a puz zling discrepancy between published data of placental protein content and our values (11). This could in part be explained by our proce dure of tissue processing which included inten sive perfusion of the intact organ with buffered saline to remove blood as complete as possible.…”

“…On the light microscopical level the LDH was shown to be located mainly in the trophoblast and 'X' cells (1), whereas the intracellular distribution is not exactly known hitherto. In a former study on placental glycolytic enzymes the total LDH activity was recovered in the supernatant (11) but in vivo the isoenzymes may nevertheless be differentially associated to membrane structures (7), the soluble fractions being washed out more readily in damaged tissue samples. There is, however, no evidence for this suggestion.…”

“…Prior to perfusion some cord blood was saved for hemoglobin and protein determination and the vessels supplying about one quarter of the placenta were ligated. After the perfusion was completed the tissue was dissected and further processed at + 4 °C exactly as described earlier (11) in order to obtain the final supernatant (FS) after 90 min centrifugation of the homogenate at 100,000 g. Hemoglobin was deter mined in aliquots of FS and in cord blood as the cyanide complex with the method outlined in Richterich (18). 2 ml FS or suitable dilutions of blood were mixed with 1 ml Drabkins solution (5) and read after 20 min at 540 nm.…”

“…The extinction coefficient of 11,000 and the molar weight of 16,114 were used to calculate the hemoglobin concentration. LDH was assayed in FS as previously described (11). Proteins and nucleic acids were determined in aliquots of the filtered homogenate.…”

Properties of Human Placental Hexokinase

“…In lens tissue of various mammalian species the particle-bound hexokinase was shown to be predominantly type I although a certain amount of type II may also be present [7], Information on type differences of human placental hexokinase is lacking hitherto. Starting from our previous observation that about 50% of the total placental hexokinase is bound to particles which are obviously mitochondria [21], we now investigated the possible existence of different isoenzymes in this organ. As was already shown by Walker et al [38] and confirmed by us, placenta does not contain glucokinase.…”