Cytochrome P-450 synthesis in vivo and in a cell-free system from rat liver.
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Biomedical subjects
Publications and source records attributed to K S Bhat.
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By using 3-amino-1,2,4-triazole, an inhibitor of haem synthesis, and 2-allyl-2-isopropylacetamide, a drug that degrades the haem moiety of cytochrome P-450, the involvement of haem in cytochrome P-450 synthesis and assembly was investigated. Phenobarbital was used to stimulate apo-(cytochrome P-450) synthesis. Degradation of preformed cytochrome P-450 haem does not result in a concomitant release of the apoprotein from the endoplasmic reticulum. The availability of haem for cytochrome P-450 synthesis in the normal animal is not rate-limiting. Prolonged inhibition of haem synthesis in vivo decreases the rate of apo-(cytochrome P-450) synthesis, although this effect is not discernible under conditions of short-term inhibition of haem synthesis. Under the former conditions exogenous haemin is able to counteract the decrease in the rate of apoprotein synthesis. In animals receiving successive injections of phenobarbital plus 3-amino-1,2,4-triazole, compared with those receiving phenobarbital only, the holo-(cytochrome P-450) content measured spectrally shows a greater decrease than could be accounted for by the decrease in the content of the total apoprotein. In addition to less haem being available under these conditions, the free apoprotein appears to have undergone some modification, such that its haem-binding capacity is considerably decreased. This particular effect could be due to a direct interaction of 3-amino-1,2,4-triazole or its metabolites with cytochrome P-450 rather than a consequence of haem deficiency. Apo-(cytochrome P-450) is capable of binding to the endoplasmic reticulum in a form and at a site, which can be reconstituted with haemin to yield the functional protein.
Effect of ingesting mega doses of ascorbic acid was studied on the leukocyte function in five normal human subjects. During the first 15 days the subjects received daily supplements of 200 mg of ascorbic acid, and during the next 2 weeks they were given 2 g of vitamin C per day. Supplementation of 200 mg as well as 2 g of ascorbic acid stimulated hexose monophosphate shunt activity of resting leukocytes indicating an increase in resting metabolism. Intakes of 200 mg of ascorbic acid per day did not affect bacterial killing by leukocytes. On the other hand, daily intakes of 2 g of ascorbic acid for 2 weeks significantly impaired bactericidal activity. Four weeks after withdrawal of the viatmin supplementation, bactericidal activity returned to normal.
The procedure that uses the response of subcutaneous connective tissue to screen dental materials and drugs will continue to be favored because of its simplicity, economy, reliability, and usefulness. The techniques of subcutaneous injection and of implantation of capsules by surgical means have many disadvantages. A modified technique is suggested; it has the ease of injection and the precision of implantation and it overcomes the difficulties inherent in both techniques.
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1. Enzymes pertinent to bactericidal activities of leucocytes were assayed in children suffering from protein-calorie malnutrition. 2. Leucocytes obtained from malnourished and control children contained similar activities for glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Granule-bound NADPH oxidase activity was low in leucocytes isolated from malnourished patients and failed to show the phagocytic stimulation which is normally seen in control leucocytes. Further, leucocytes obtained from malnourished patients did not release the acid phosphatase from lysosomes during phagocytosis, unlike those from controls. 3. Treatment of the malnourishment with a diet high in calories and protein resulted in significant increase in the activities of glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and NADPH oxidase and in releasing the acid phosphatase from the lysosomes into the supernatant fraction during phagocytosis. 4. The significance of these enzyme changes are discussed in relation to the increased susceptibility of these patients to infection.
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