Abstract
The activities and the content of enzymes involved in mixed function oxidase systems (cytochromes P-450 and b5, NADPH-cytochrome c reductase and NADH cytochrome b5 reductase) in microsomes from 114 human placentae were found to increase from the 34th up to the 38th–39th week of gestation and later to decrease until the 43rd week. Such a process can be related to the following: (i) the phospholipid content of microsomal membranes; (ii) the protein synthesis possibly induced by steroids such as androstenedione and testosterone.