Studies on the structure of collagen. 3. On the presence of alpha-keto acids in collagen

The reaction of amines with carbonyls: its significance in the nonenzymatic metabolism of xenobiotics

The studies cited above indicated that many carbonyl amine reactions can alter both in vitro and in vivo rates of xenobiotic metabolism. The carbonyl amine reaction may be enzymatic or nonenzymatic and in most instances is readily reversible with few examples of the isolation and identification of the Schiff bases (azomethine). Endogenous primary amine and amines generated by metabolic N-dealkylation can react with biogenic ketones and aldehydes and under selected physiological conditions give further condensation products. The new products in most instances alter the biological activity and/or toxicity. It is apparent that these findings can be extended to carbonyl hydrazine reactions. The rates of reaction for simple alkyl and aryl hydrazine are more rapid and the products of these reactions and more stable, with the condensation products of alpha-keto acids being isolated and characterized the most frequently. The further reaction of hydrazones to yield condensation products is also observed with selected hydrazines such as hydralazine. It is now clear that the inherent toxicity of many exogenous ketones and aldehydes exists. Many of these toxicities are due to the reactions which occur with the amino groups of amino acids and proteins. The condensation reactions in most instances are readily reversed and are only dependent on the physiological concentration of aldehydes of ketones. However, there are a number of ketones and aldehydes, some of which are metabolically produced that are capable of forming azomethine intermediates which are not readily reversed under physiological conditions. There are an increasing number of examples of further nonenzymatic condensations which result in stable products which can alter xenobiotic metabolism.