Sex differences in activity of glucose 6-phosphate dehydrogenase from cultured human fetal lung cells despite X-inactivation

In a previous report, it was noted that glucose 6-phosphate dehydrogenase (G6PD) specific activity was approximately 45% higher in fibroblasts cultured from female fetal lung than in fibroblasts from male fetal lung. This sex difference was nullified during the first postnatal weeks by an abrupt rise in G6PD activity in cultured male lung rather than by any changes in G6PD activity in cultured female lung. No sex differences for G6PD activity were found in fetal or postnatal cultured skin (Steele and Owens, 1973). In the present report, analysis of the G6PD phenotype of clones derived from skin and lung fibroblasts from a 14-week fetus heterozygous for the AB electrophoretic variants of G6PD indicates that in these fetal cells only one X chromosome is active. Therefore, the sex differences in the specific activity of G6PD in fetal lung cells cannot be attributed to lack of X-inactivation in the female but must result from yet undefined regulatory mechanisms operative in the male.This work was supported in part by HRSF of Pittsburgh Grant No. L-22, NIH GRS Grant No. 5-S01FR05507, National Cancer Institute Grant No. R01 CA12113, and NIH Grant No. HD 05465.