Previous studies have implicated the reticuloendothelial cells of the liver in certain aspects of steroid metabolism. The similarity in the metabolism of steroids and polycyclic hydrocarbons suggested that the nonparenchymal cells possibly play a role in these areas. The present study presents evidence that at least one of the microsomal NADPH-requirig enzymes, benzpyrene hydroxylase, is present in nonparenchymal cells and, furthermore, is "inducible." In adult rats treated with 3-methylcholanthrene or beta-naphthoflavone, the nonparenchymal cells exhibited increases in benzpyrene hydroxylase activity of 17-fold and five-fold, respectively. Treatment with phenobarbital resulted in only a slight increase in enzyme activity. Enzyme activity in parenchymal cells under similar conditions was increased sixfold and fivefold by 3-methylcholanthrene and beta-naphthoflavone, respectively, but not by phenobarbital.

Animals↗

PubMed1972

Ontogenetic changes of proteins of endoplasmic reticulum.

The proteins of the smooth and rough endoplasmic reticulum from fetal, immature, and adult male rats were compared after incorporation of two radioactively labeled precursors, (14)C-labeled amino acids and delta-aminolevulinic acid-(3)H by means of gel electrophoresis. The labeling patterns indicated that protein components present in two major electrophoretic bands underwent significant synthesis in fetal tissue while three actively incorporating protein bands were noted in adult tissue. Although the uptake of the amino acids-(14)C decreased for the smooth and rough elements of the endoplasmic reticulum as a whole during liver development, the qualitative patterns were not significantly different in adult and fetal livers. The over-all incorporation (disintegrations per minute per milligram protein) of the heme precursor into the smooth and rough elements also did not change with development. However, a change was noted in the distributional electrophoretic patterns with development. The estimation of molecular weight (by disc electrophoresis) and the incorporation of the heme precursor suggested the similarity of the two major protein bands to cytochrome P-450 and cytochrome b(5), components of the endoplasmic reticulum, thought to be involved in the mixed-function oxidase system. The evidence indicated that in fetal liver, at a time when the oxidase capability was low, the amino acid incorporation into these two protein groups was the same as in the adult. The incorporation of the heme moiety, however, was different, decreasing in the cytochrome b(5) region and increasing in the cytochrome P-450 region during development. These results correlate with the increase in oxidase activity associated with liver development.

Amino Acids↗

PubMed1972