STUDIES ON THE DISTRIBUTION AND CHARACTERISTICS OF NEW MAMMALIAN SELENIUM-CONTAINING PROTEINS

It has now been established that the essential effects of selenium in mammals are owing to the presence of several biologically active selen ium compounds. Seleno-enzymes identified so far include several glutat hione peroxidases and the type 1 iodothyronine de-iodinase. Some other selenoproteins have been sequenced and characterized. After in vivo l abelling of rats with Se-75 and protein separation using gel electroph oretic methods, more than 25 selenium-containing proteins or protein s ub-units were detected. Some of the results of the investigations on t hese compounds are summarized and discussed here. By determining the p attern in a large number of tissues information on the distribution of the some of the selenium-containing proteins was obtained. Their biol ogical summarized. significance is not yet known but several findings indicate that some of these proteins may have important functions, esp ecially in the brain and the endocrine and reproductive organs. More d etailed information is already available on a 34 kDa-protein found in the testis and spermatozoa. Studies on the effects of dosage and chemi cal form of dietary selenium indicated that the tissue levels of the s eleno-enzymes are homeostatically controlled and cannot be increased b y additional supply. The increase in the tissue selenium observed with high selenium intake was found to be mainly caused by the non-specifi c incorporation of the element into a large number of proteins. The fo rmation of most of the other selenium-containing proteins has priority over that of the cytosolic and plasma glutathione peroxidases. Thus t he selenium requirement, which was calculated for optimum plasma gluta thione peroxidase activity, also covers the amounts needed for normal levels of the other biologically important selenium compounds.