ACTIVITY OF ENZYMES OF ENERGY-METABOLISM IN SINGLE HUMAN PREIMPLANTATION EMBRYOS

A method was developed to measure the activities of enzymes in extract s from single human preimplantation embryos. The method permits the an alysis of two enzymes plus appropriate controls in an extract from a s ingle embryo, and was used to investigate the control of energy metabo lism during the development of human embryos from the two-cell to the blastocyst stage. Hexokinase (HK), 6-phosphofructokinase (PFK), pyruva te kinase (PK), fructose-1,6-diphosphate aldolase (ALD), glucose phosp hate isomerase (GPI), lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G6PDH) and 2-oxoglutarate dehydrogenase (ODH) were all detectable, whereas glycogen phosphorylase (GP) was not. The enzyme a ctivities of ODH, PFK, LDH, PK, GPI and G6PDH, averaged over all stage s of development from the two-cell to blastocyst stage (days 2-6 after insemination), were 3.5, 6.6, 15, 69, 73 and 87 times greater than HK , respectively. The activity of ALD was very similar to that of HK. Th e activities of ALD, GPI, PFK, PK and LDH showed no significant variat ion with stage of development, although the activity of GPI fell signi ficantly from the four-eight cell to the eight-sixteen cell stage (P < 0.05). HK activity decreased from the two-eight cell to the eight-six teen cell (P < 0.05), and increased significantly from the eight-sixte en cell to the blastocyst stage (P < 0.01). The overall relationship b etween hexokinase activity and stage approached significance (P = 0.05 9, one-way analysis of variance). The activity of G6PDH decreased sign ificantly with development (P < 0.001, one way analysis of variance). The data suggest that hexokinase plays a key role in the control of gl ucose utilization in the early human embryo, although a role for PFK i s not ruled out. The fact that GP could not be detected suggests that the breakdown of glycogen contributes very little to the energy metabo lism of the human preimplantation embryo. The absolute and relative en zyme activities in the human embryo are comparable to those in adult t issues, although that of G6PDH is very high and that of GP is low. The activities of the enzymes are discussed in relation to the changes in pyruvate and glucose uptake and the production of lactate, during ear ly human development.