A marked increase in latency of fetal rat liver UDP-glucuronosyltransferase accompanies the fluidization of the microsomal membrane in the perinatal period

The activity of rat liver microsomal uridine diphosphate glucuronosyltransferase towards 4-methylumbelliferone (4-MU-UDPGT) increased markedly between day 18 of fetal life and day 1 after birth. This increase in UDPGT activity resulted largely from a gradual increase in the fraction of enzyme activity which was detected after pretreatment of microsomes with digitonin ('latent' activity). The latent fraction of 4-MU-UDPGT activity approached at birth the values obtained for adult rat liver. This perinatal increase in latency of 4-MU-UDPGT activity may be associated with the concurrent fluidization of the microsomal membrane which is observed in the perinatal period.