Reflections on the role of the thiol group in biology.

This essay is concerned with the role of the thiol or sulfhydrvl group in cellular function and metabolism and with the important investigations over many years that have led us to a better understanding of the importance of this molecular moiety that plays such a vital role in biology. The tools for measuring the SH group and for inhibiting or regenerating it will be discussed as will its essential role in the actions of many enzymes. The importance of the thiol group in glycolysis and in energy production by mitochondria will be emphasized. Of special interest at present is the fact that certain low molecular weight SH-containing substances can mimic some of the actions of insulin and may become of benefit in the treatment of diabetes mellitus. Finally, the toxic effects of oxygen on metabolism and function will be discussed with particular reference to the possibility that oxidation of thiol groups may play a role in the manifestations of oxygen toxicity.