Non-enzymatic glycation of bio-molecules by sugars and sugar metabolites
The glycation reaction is an intricate set of reactions in which the initial step is reversible formation of Schiff's base by nucleophilic attack of the amino group on the carboxyl group of sugar or their metabolites, which then rearranges itself to form a stable Amadori product. The Amadori product then undergoes a series of auto-condensation reactions to form what are known as ‘Advanced Glycation Endproducts or AGE’. Long lived proteins in the body such as albumin and collagen, both widely studied and abundant proteins, have been shown to be affected by glycation causing both a loss of their structure and function as well as leading to diabetic complications such as retinopathy, angiopathy, etc. to name a few. AGE have been implicated in pathology of complications of diabetes such as diabetic angiopathy, diabetic retinopathy, diabetic neuropathy, Alzheimer's disease, heart diseases and recently suspected to be involved in Autism. This current dissertation demonstrates the effects of glycation on the physical and kinetics characteristics of human erythrocyte anti-oxidant enzyme Glutathione Peroxidase (GPx) by various sugar and sugar like compounds. Results from UV and activity profiles showed that all the sugars tested glycated the enzyme with MG and GA being the potent glycators. Also the kinetic characteristics were changed upon incubation in general and that MG followed by GA had more pronounced effect. CD spectroscopy revealed the loss of α-helical secondary structure upon glycation by MG and GA. pH profiles showed that the glycated enzyme had optimum activity in the alkaline pH and temperature profiles showed upon glycation the heat stability of the enzyme had decreased. Mass spectrometry studies identified the site of glycation of MG to be Arg-177 residue which being close to the catalytic site is thought to be the reason for loss of activity upon glycation. ^ The intake of branched chain amino acids (BCAA) as a nutritive supplement has become popular among athletes to build lean muscle and also in those suffering from muscle loss and fatigue. In this report we show that under physiological conditions of temperature and pH, BCAA can participate in nonenzymatic reactions forming AGE. Of the three sugars tested glyoxal was most reactive followed by methylglyoxal and DL-glyceraldehyde. The reactivity of L-leucine, L-isoleucine and L-valine were found similar with each of the sugars. These findings suggest that the intake of BCAA supplements must be carefully considered in hyperglycemia. ^ Hyperhomocysteinemia is a condition where there are elevated serum and plasma levels of amino acid homocysteine due to the improper metabolism of amino acid methionine. Studies have shown that in diabetes, hyperhomocystenemia is related with micro- and macrovascular complications such as diabetic retinopathy, diabetic neuropathy, and microangipathy. So far studies on hyperhomocysteinemia have focused on developing analytical methods to monitor the free and total homocysteine levels in serum and plasma and there are no methods for analyzing the AGE. Here we report a new and easy to use HPLC method for the analysis of AGE of homocysteine and also that among the sugars tested the three carbon sugars methylglyoxal, glyoxal and DL-glyceraldehyde were the most reactive in that order respectively.^
Chemistry, Biochemistry|Health Sciences, Pathology
"Non-enzymatic glycation of bio-molecules by sugars and sugar metabolites"
Dissertations and Master's Theses (Campus Access).