Discoveries of vitamin B12 and selenium enzymes

My undergraduate education at Cornell University was followed by graduate studies on methane fermentations under the guidance of H.A. Barker at the University of California, Berkeley. My Ph.D. degree was granted in June 1949. Two anaerobic microorganisms isolated from the mud flats of San Francisco Bay served as sources of biochemical research material for later studies at the National Institutes of Health in Bethesda. These organisms, Methanococcus vannielii and Clostridium sticklandii, proved to be especially rich sources of selenium-dependent enzymes and seleno-tRNAs. New B12 coenzyme-dependent enzymes that catalyzed intermediate steps in the anaerobic conversion of lysine to fatty acids and ammonia were isolated from C. sticklandii and characterized. My research efforts since 1970 have dealt primarily with various aspects of selenium biochemistry. We have shown that selenium is an essential constituent of several enzymes in prokaryotes. Se is present in these either as a selenocysteine residue in the protein or alternatively, in a few molybdoenzymes, as a component of a bound cofactor. Recent studies with a human adenocarcinoma cell line led to the unexpected discovery that selenocysteine occurs in mammalian thioredoxin reductase. The selenium located in a redox center of this enzyme is essential for catalytic activity.