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.