GTF from brewers' yeast

The nutritional deficiency of chromium has been linked with impaired glucose tolerance, and more recently has been implicated in cardiovascular disease. It was believed that a biologically potent form of chromium existed as a coordination complex with nicotinic acid and various amino acids. The biologically active chromium complex was termed glucose tolerance factor (GTE) due to the curative effect on rats raised on a chromium deficient diet resulting in impaired glucose tolerance. The most studied source of GTE has been brewers' yeast although little has been learnt regarding the structure of GTE. The aim of this thesis was to isolate and characterize GTF. An existing in vitro assay system for GTE has been developed and is reported in this thesis. The assay was based on the anaerobic oxidation of 14 C-glucose by yeast (Saccharomyces cerevisiae) and its stimulation by GTF. Brewers' yeast was used as a starting material for the isolation of GTE. A defined synthetic Medium was eventually used for yeast culture, in order to establish that GTF was produced by yeast and not derived from culture medium components. GTF was isolated from yeast grown in synthetic medium and in higher yield when chromium was present. Low levels of chromium were found to inhibit yeast growth. A biologically active cationic fraction extracted from yeast was purified by chromatography. Nuclear Magnetic Resonance spectroscopy and other instrumental techniques indicated that the isolated material was a small lysine peptide devoid of chromium which could be likened to a class of basic hypoglycemic, agents. It was concluded that, as recent clinical trials reported in the literature indicated a division between the effect of chromium supplementation, and supplementation with high chromium yeast, GTF isolated from yeast grown in presence of chromium represents an interesting hypoglycemic agent.