Glucose metabolism, chromium biological activity

It appears that chromium(III) is an essential trace element in mammalian metabolism and, together with insulin, is responsible for the clearance of glucose from the blood-stream. Tungsten too has been found to have a role in some enzymes converting CO2 into formic acid but, from the point of view of biological activity, the focus of interest in this group is unquestionably on molybdenum. 

In humans and animals, chromium(ni) is an essential nutrient that plays a role in glucose, fat, and protein metabolism by potentiating the action of insulin (Anderson 1981). The biologically active form of chromium, called glucose tolerance factor (GTF), is a complex of chromium, nicotinic acid, and possibly amino acids (glycine, cysteine, and glutamic acid). Both humans and animals are capable of converting... 

Chromium(III) is an essential nutrient required for normal energy metabolism. The National Research Council (NRC) recommends a dietary intake of 50-200 ig/day (NRC 1989). The biologically active form of an organic chromium(ni) complex, often referred to as GTF, is believed to function by facilitating the interaction of insulin with its cellular receptor sites. The exact mechanism of this interaction is not known (Anderson 1981 Evans 1989). Studies have shown that chromium supplementation in deficient and marginally deficient subjects can result in improved glucose, protein, and lipid metabolism. 

Finally, it should be noted that this chemistry may have biological relevance. Several metalloenzymes are believed to contain more than one metal ion bound at the active site. One relevant example is the glucose tolerance factor (GTF) which is important for the metabolic degradation of glucose (398-401). GTF is a low-molecular-weight protein which contains chromium(III). Its structure is not known, but it has been suggested that the active site contains a dinuclear chromium(III) complex (401). The fact that hydroxo-bridged dinuclear chromium(III) complexes exhibit reactions which are often very fast compared with those observed for the parent mononuclear species seems to support such a proposal. 

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