Development of methyltransferase activities of human fetal tissues

Abstract

N5-Methyltetrahydrofolate-homocysteine methyltransferase specific activity was higher in fetal (2nd trimester) human liver and kidney (4.70 ± 0.20 and 7.25 ± 0.23 nmol/mg protein/hr) than in mature human liver and kidney (1.30 ± 0.16 and 0.76 ±0.18 nmol/mg protein/hr). During the same period, there was a significant correlation of decreasing specific activity of this enzyme in fetal brain with increasing crown- rump length (r = —0.72; P < 0.005), reaching the specific enzymatic activity of adult brain (1.37 ± 0.26 nmol/mg protein/hr). Betaine-homocysteine methyltransferase specific activity was lower in fetal liver and brain (1.82 ± 0.21 and 0.20 ± 0.05 nmol/mg protein/hr) than in mature liver and brain (7.78 ± 1.89 and 0.37 ± 0.07 nmol/mg protein/hr). During the same period, there was a significant correlation of increasing enzymatic activity in fetal kidney with increasing crown-rump length (r = 0.80; P < 0.005) toward the mean specific activity of mature kidney (22.6 ± 2.0 nmol/mg protein/hr). Serine tetrahydrofolate 5,10-hydroxymethyltransferase specific activity showed no significant difference between fetal and mature liver and kidney; however, the fetal brain showed a significant correlation of decreasing specific activity of this enzyme with increasing crown-rump length (r = —0.69; P < 0.005). The specific activities of betaine-homocysteine methyltransferase and serine-tetra- hydrofolate 5,10-hydroxymethyltransferase in the liver of the neonate was not different from that in the mature liver. N5-Methyltetrahydrofolate-homocysteine methyltransferase in neonatal liver attained a specific activity similar to that found in mature liver before cystathionase did. Cystathionase in 2nd trimester human fetal kidney, in contrast to cystathionase in human fetal liver and brain, already has attained two-thirds of the mean specific activity of mature kidney. © 1973 International Pediatric Research Foundation, Inc.