THE ENZYMATIC FORMATION OF HYDROXAMIC ACIDS FROM GLUTAMINE AND ASPARAGINE

Abstract

Although glutamine and asparagine have a wide distribution in nature, heretofore the only metabolic function ascribable to them on the basis of known enzymatic processes has been their participation in the metabolism of ammonia (1, 2).We have recently reported the formation of hydroxamic acids by the enzyme-catalyzed replacement of the amide groups of glutamine and asparagine with hydroxylamine (3-5).The same enzyme extract also catalyzes the exchange of the amide group of glutamine and asparagine with (isotopic) ammonia ( 6).The process would have considerable biological significance if it could be shown that amino acids can participate in an analogous reaction to form peptide bonds.The enzymatic formation of hydroxamic acids from glutamine and asparagine described here is different from the enzymatic synthesis of y-glutamohydroxamic acid from glutamic acid (7, 8).The latter reaction, which has been used as a model for glutamine synthesis, requires the utilization of adenosinetriphosphate as an external source of energy, whereas the formation of y-glutamo-and /3-aspartohydroxamic acids from the corresponding amides proceeds without the utilization of energy-rich phosphate bonds.The enzyme preparations which synthesize the hydroxamic acids from the amides and hydroxylamine can also split hydroxamic acids.The enzyme systems are widely distributed in microorganisms.In the present report the enzymatic synthesis of glutamo-and aspartohydroxamic acids from the two natural amides by enzymes occurring in cell-free extracts of Proteus vulgaris X-19 is described in detail.Some observations on the synthesis of glutamine from glutamic acid are also included. EXPERIMENTALFor the estimation of the hydroxamic acids, the color reaction with ferric chloride as used by Lipmann and Tuttle (9) was employed.The synthetic hydroxamic acids were prepared to serve as standards.