Oxidative deamination of glutamate and transdeamination through glutamate

Abstract

Rat liver mitochondria are able to produce ammonia from glutamate at a steady rate under the conditions described. A system generating ADP from ATP is necessary for the continual deamination of glutamate. Maximum stimulation is reached with a hexokinase-glucose system in the presence of 0.2 m m ATP. The phosphorlyation control ratio (ammonia produced in the presence of hexokinase and glucose divided by ammonia produced in their absence) is of the order of four. Mitochondria incubated with glutamate at 38 ° for 30 minutes in the medium plus 0.5 m m ATP, retain the ability to increase their rate of glutamate deamination on the subsequent addition of hexokinase and glucose; they lose this ability if incubated for 20 or 40 minutes at 38 ° as a sucrose suspension. 2,4-Dinitrophenol increases the rate of ammonia production from glutamate and thus abolishes a rate-limiting step. Ammonia is produced from glutamate at both 25 ° and 38 ° but at a faster rate at the higher temperature. The phosphorylation control ratio in terms of ammonia is greater at 38 ° than at 25 °. Transdeamination of alanine and aspartate by rat liver mitochondria may be mediated by the addition of α-ketoglutarate or glutamate. Excess α-ketoglutarate (greater than 0.5 m m) inhibits the production of ammonia from alanine and aspartate.