Developmental, tissue-specific, and sex differences in activity among three enzymes from human erythrocytes and cultured fibroblasts.

Abstract

G6PD specific activity (S.A.) was significantly greater in human females than in males, both in fresh erythrocytes from newborns and in prenatal cultural lung. The sex difference in erythrocytes was nullified by 6 years of age via a reduction of G6PD S.A. in the female relative to the male. The sex difference in prenatal lung was nullified during the first month of postnatal life by an abrupt rise of G6PD S.A. in the male rather than by any postnatal change in the female. No sex difference was found for G6PD in cultured skin or for LDH and HGPRT in any of the tissues studied. Qualitative and quantitative tissue-specific and developmental differences were found among G6PD, LDH, and HGPRT in cultured skin and lung. Our data suggest (1) that cultured fibroblasts still can reflect the tissue-specific, developmental, and sex differences of their origin and (2) that sex differences for X-linked loci such as G6PD do not necessarily imply escape of the locus from X-inactivation in the female but rather may result from other unknown regulatory mechanisms in either sex.