Acetyl glutamate--a model of signals for intracellular proteolysis

The proteolysis at neutral pH of mitochondria from liver and brain is more marked in isolated preparations than "in vivo" indicating activation of proteases or inactivation of repressors during isolation. Acetyl glutamate (AG), found in liver mitochondria of ureotelic animals, plays a crucial role as activator of carbamylphosphate synthetase. Since AG levels change under a number of conditions, we checked for an AG deacylase in mitochondria, for otherwise AG must be exported and destroyed by cytosol deacylases. We noted on incubation of mitochondrial extracts with AG an increase in trichloracetic acid-soluble ninhydrin-reacting material but not in acetate liberation, indicating activation of proteases. This was checked with 14C-labelled mitochondria. Under certain conditions AG and other acyl aminoacids stimulate approximately 5 to 20% the proteolysis with rat live and with brain mitochondria.