Liver Microbodies

A response to exposure to certain foreign compounds, which occurs predominantly in the liver is the phenomenon of peroxisomal proliferation. Peroxisomes (microbodies) are organelles found in many cell types, but especially hepatocytes. Repeated exposure of rodents to certain... 

Baudhuin P, Muller M, Poole B, de Duve C (1965) Non-mitochondrial oxidizing particles (microbodies) in rat liver and kidney and in Tetrahymena pyriformis. Biochem Biophys Res Commun 20 53-59... 

Figure 47-4 Portions of two human liver cells showing the relationship of the organelles and a typical bile canaliculus (BC). Arrowheads indicate light junctions, N, Nucleus M, mitochondria Mb, microbody G, Golgi SER, smooth endoplasmic reticulum L, lysosome g, glycogen. (From Zakim 0, Boyer TD. Hepatology A tejctbook of liver disease, 3rd ed. Philadelphia WB Saunders, 1996 20.)...

Han liver and described as microbodies (Hruban and Rechcigl, 1969). Subsequently they were isolated on sucrose gradients and intensively studied by de Duve and his colleagues (de Duve and Baudhuin, 1966). Of particular interest was that the microbodies had been shown to be bound by a single membrane they were 0.5-1 /am in diameter, and in sucrose gradients they achieved an equilibrium density of 1.25 g/cm . 

Rhodin described in 1954 a newcellular organelle that he discovered in the proximal tubular epithelium of the kidney and called a microbody [263]. At first microbodies were believed to exist only in a few tissues such as liver kidney, and tetrahymina. It is now apparent that they exist almost in every vertebrate tissue and in many plants. 

Microbodies cannot be seen with the light microscope on electron micrographs they appear like small round bodies (5 p in diameter in liver) with a single membrane surrounding a homogeneous electron-dense mass. 

It has been shown that these organelles contain peroxidase, catalase, uricase, and a number of other oxidases, such as D amino oxidase, L-hydroxy acid oxidase, and even isocitrate dehydrogenase [264]. Because of their content in peroxidase, microbodies have been renamed peroxisomes. Nothing is known of their role in cellular physiology. Usually on the basis of circumstantial evidence they have been suspected to play a role in purine (because of the presence of xanthine oxidase and allantoinase in the kidney and liver of chicken microbodies), cholesterol, lipid, and steroid metabolisms, gluconeogenesis, photosynthesis, and respiration. 

Svoboda and his associates [81] investigated the disappearance of microbodies after their multiplication under the influence of various chemical stimuli and concluded that engulfment in autodigestive vacuoles could only, in part, explain their dissolution. In conclusion, there is ample evidence that the liver catabolizes all or most of its protein, and that under the influence of special stimuli it catabolizes some proteins selectively. 

Oral administration of plasticizers, fats and other chemicals including hypolipidaemic drugs to rodents causes a proliferation of microbodies in the liver called peroxisomes which are considered by some authors to be linked to the formation of liver tumours. 

Up until recently it had always been considered that /3-oxidation was confined to mitochondria. Although animal mitochondria do contain all the enzymes necessary and are a major site for )8-oxidation, other subcellular sites, such as the microbodies, are implicated. Peroxisomes or glyoxysomes, together are often referred to as microbodies. They contain a primitive respiratory chain where energy released in the reduction of oxygen is lost as heat. The presence of an active /3-oxidation pathway in microbodies was first detected in glyoxysomes from germinating seeds by de Duve in 1976. Since that time the various enzymes involved have been purified and characterized for microbodies from rat liver. 

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