The liver microsomal monooxygenase system in the human fetus: distribution in different centrifugal fractions.

Abstract

The distribution of microsomal, mitochondrial, and lysosomal enzyme activities in different centrifugal fractions of the human fetal liver was studied. Sixty to 70 per cent of the total activities of glucose‐6‐phosphatase and reduced nicotinamide adenine dinucleotide phosphate (NADPH)‐cytochrome C reductase and the amount of cytochrome P‐450 was found in the 200 × g pellet; 10 to 15 per cent was recovered in the 105,000 × g pellet while the rest appeared in the 9,000 × g pellet. Succinic dehydrogenase activity was found only in the 200 × g and 9,000 × g pellets while acid phosphatase was found in all pellets. The 105,000 × g pellet contained only 11 per cent, however. These results were in agreement with the electron microscopic findings. The 200 × g pellet contained hepatocytes with endoplasmic reticulum, erythrocytes, hematopoietic cells, and naked nuclei in equal proportions. The 9,000 × g pellet predominantly contained mitochondria and cisternae of (unbroken) endoplasmic reticulum, while the 105,000 × g pellet was composed of microsomal vesicles of different appearance and free ribosomes. The levels of NADPH‐cytochrome C reductase and cytochrome P‐450 per gram of liver in human fetuses were comparable to those reported previously for adult human liver. In contrast, the activities (per gram of liver) of glucose‐6‐phosphatase and succinic dehydrogenase were lower and that of acid phosphatase higher in human fetuses compared to adults. The low recovery of microsomes from human fetal liver and the pattern of distribution of the enzymes in the different fractions of the liver are discussed in relation to the electron microscopic findings.