ENZYMATIC MECHANISM TO CONTROL NONENZYMATIC GLYCATION

点击翻译按钮获取中文摘要

Glucose is an essential macronutrient of most mammalian cells where it functions as the main source of energy and carbon. However, at high concentration glucose can have detrimental effects on cells. This is most dramatically manifested in diabetes mellitus where chronic hyperglycemia leads to many diabetic complications including: retinopathy, vascular disease, neuropathy and nephropathy. There is substantial evidence to suggest that some of the deleterious effects of hyperglycemia are caused by the non- enzymatic glucosylation of proteins wherein glucose reacts with lysine residues to form fructoselysine (FL). This early, reversible, glucosylation product subsequently undergoes a series of further reactions leading ultimately to the formation of the irreversible Advanced Glycation Endproducts (AGE's). Both the early and advanced glucosylation products have adverse effects on cell function (especially in the kidney) and AGE accumulation has been documented in many tissues in aging and diabetes. Recently we discovered an apparently ubiquitous enzyme (Fructoselysine Phosphotransferase, FLPT) which phosphorylates fructoselysine on proteins to fructolysine-3-phosphate (FL 3P). This modification of FL subsequently leads to its spontaneous decomposition and the regeneration of an unmodified lysine residue. We postulate that the function of FLPT in mammalian cells is to breakdown FL thus reversing the nonenzymatic glucosylation process at the earliest possible point of intervention. Furthermore we propose that variable efficiency of the FLPT-mediated deglucosylation may be a determinant of the susceptibility of individuals to diabetic complications and the rate of normal aging. We intend to explore these hypotheses through two specific aims: 1) Purification of the fructoselysine phosphotransferase enzyme (from human erythrocytes) and its complete molecular characterization 2) Assessment of the activity of FLPT pathway in erythrocytes from populations of diabetic patients with accelerated and retarded rates of development of diabetic nephropathy.