Question

Glutamate dehydrogenase is significant in the mitochondrial matrix. Suggest 1 explanation

Hence, what is the reaction catalyzed by CPS I and what is the role of aspartate in urea cycle?

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Answer 1

Glutamate dehydrogenase plays an major role in amino acid metabolism. It is a zinc protein requires NAD1 and NADP1 as a coenzyme, and present in high concentrations in mitochondrial matrix . It catalyzed the oxidative deamination of L- glutamate to alpha keto glutarate and NH3. An experimental study of glutamate dehydrogenase in mitchondrial matrix shown that, about 25% of the NADH-GDH activity was solubilized from purified mitochondria after a simple osmotic shock treatment of cell. Whereas the remaining 75% of the activity was associated with the mitochondrial membrane function. When the lyed mitochondria , mitochondrial matrix or mitochondrial membrane fraction was used as a the source of NADH-GDH.

CPS catalyzed the reaction-  

NH4 + bicarbonate+ 2ATP with NAG , k+ and Mg binding results carbonyl phosphate +2ADP+pi+ 2H+ . Nag binding changes the confirmation and subunit structure of CPSI, with preponderance of the monomers. There are two immunologically distinct carbonyl phosphate synthases, one is CPSI and other is CPSII. CPSI involves in ureagenesis, uses NH3 exclusively as the nitrogen donor, and requires binding of NAG for activity.

Role of aspartate in urea cycle - Aspartate , which acts as a nitrogen donor in the urea cycle reaction catalyzed by argininosuccinate synthetase in the cytosol, is formed from oxaloacetate by transamination from glutamate. The other product of this transamination is alpha- ketoglutarate, another intermediate of the citric acid cycle.