INSITU GLUCOSE-6-PHOSPHATE-DEHYDROGENASE ACTIVITY DURING DEVELOPMENT OF PREIMPLANTATION MOUSE EMBRYOS

Glucose-6-phosphate dehydrogenase activity was analysed cytophotometri cally in oocytes and pre-implantation embryos of mice. A bimodal distr ibution pattern was not found. Therefore, female and male embryos coul d not be discriminated on the basis of linkage of the enzyme with the X-chromosome during the pre-implantation period. The dehydrogenase act ivity in ovulated eggs and pre-implantation embryos up to the 8-cell s tage was 65% of that present in follicular oocytes. In morulae and bla stulae, the activity was further decreased to a level that was only 10 -20% of the activity present in oocytes. The dramatic decrease in dehy drogenase activity could not be explained by modulation of the enzyme molecules, because K(M) values did not vary strongly. It is unlikely t hat the abundant activity of glucose-6-phosphate dehydrogenase in oocy tes is due to high activity of the pentose phosphate pathway because o f the low activity of 6-phosphogluconate dehydrogenase, the next step in this pathway. It is concluded that high activity of glucose-6-phosp hate dehydrogenase in oocytes is needed for keeping oocytes viable, an d for generation of NADPH which is important for the fertilization pro cess.