Abstract
In the rat testis, 7 days after hypophysectomy, the microsomal content of cytochrome P-450 decreased to a negligible level. The sodium dodecyl sulfate gel electrophoresis of the microsomal preparation did not reveal a decrease in apocytochrome P-450; however, in this preparation, heme was undetectable. The latter did not reflect decreases in the activities of the heme biosynthesis enzymes. Also, an increase in heme oxygenase activity did not appear responsible for the suppression of the cytochrome levels. The cellular basis for the depression of the cytochrome was explored by measuring the incorporation of [14C]delta-aminolevulinate into the testicular microsomal and mitochondrial hemoproteins, and determining the relative affinity of microsomal heme for the endoplasmic reticulum membranes. In comparison with the sham-operated animals, in hypophysectomized rats, the specific 14C activity of heme in mitochondrial fraction was not decreased; however, that of the microsomal fraction was markedly reduced. The latter appeared to reflect a lowered binding affinity of the apoprotein moiety of cytochrome P-450 for heme. The treatment of hypophysectomized rats with human chorionic gonadotropin partially restored the normal level of the cytochrome. It is suggested that the anterior pituitary hormones control the level of cytochrome P-450 in the testis through factors which do not involve the production of heme; rather, the control appears to involve the processes of assembly of the hemoprotein and the association of the heme molecule with the apoprotein.
Highlights
In the rat testis, 7 days after hypophysectomy, the activity in the testismay be dependent on thepresence of the microsomal content of cytochrome P-450decreased to pituitary gonadotropins (8)
The cellular basis for the depression of the cytochrome was explored by measuring the incorporation of [14C]&aminolevulinate intothetesticularmicrofindings suggestthe possibility that in thheypophysectomized animals the depression in the cytochrome P-450 levels may not represent the impaired synthesis of cellular proteins in general, and thoseof the heme pathwaeynzymes in particular; somal and mitochondrialhemoproteins, and determin- rather, an alternative mechanism could be involved in the ing the relative affinity of microsomal heme for the degradation in these animalsof the hemoprotein
The cellular basis for the loss of testicular cytochrome P450 in hypophysectomized ratshas beenexplored inthe present study as it relates to heme metabolic processes
Summary
We show the effects of hypophysectomy and administration of hCG to hypophysectomizedrats onthe activities of the enzymes of the heme biosynthetic pathway: ALA synthetase, ALA dehydratase, and ferrochelatase. The administration of hCG t o hypophysectomized rats partially restored cytochromeP-450 to the normal level and fully restored the microsomal heme concentration. Cytochrome P-450 and the total heme contents were measured in the microsomal fraction These measurements were carried out as detailed under “Experimental Procedures.”.
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