Catabolism in vitro of cholesterol: Some comparative aspects

Abstract

In further investigation of the cholesterol oxidase system, found principally in liver, which is capable of oxidizing the three terminal carbon atoms of the side chain to carbon dioxide, several sterols were tried with liver mitochondria from various species of animals. Terminally labeled (C 26) 3α,7α,12α-trihydroxycoprostane, 3α,7α,12α-trihydroxy-24-ketocoprostane and 3α,7α,12α,24ξ-tetrahydroxycoprostane were tried along with cholesterol. It was found that rat liver mitochondria preparations oxidized 3α,7α,12α-trihydroxycoprostane in vitro more readily than the other two coprostane derivatives while with mouse, monkey, and human liver mitochondria, 3α,7α,12α-trihydroxy-24 ketocoprostane was more readily oxidized. The mitochondria of liver mitochondria from the rat, chicken, turtle, alligator, crocodile, rabbit, hamster, and guinea pig were tested for their ability to oxidize the terminal side-chain carbon atoms of cholesterol and 3α,7α, 12α-trihydroxycoprostane to carbon dioxide. Rat and chickens showed considerable ability to oxidize both sterols. Rabbit, hamster, and guinea pigs had a very much reduced ability to oxidize cholesterol and a somewhat reduced ability to oxidize 3α,7α,12α-trihydroxycoprostane. The turtle, crocodile, and alligator showed a very small oxidizing ability for cholesterol and practically none for the trihydroxycoprostane. This is consistent with the known formation of 27-carbon compounds in the bile of these species. Mitochondria from monkey spleen and early embryonic chick and rat livers had a small but positive oxidizing ability for the cholesterol terminal carbon atoms. The operation of a species-dependent factor in the oxidation of sterols by various species may produce a problem in further investigation of these reactions.