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The degradation of thyroliberin (2) to its component amino adds by the soluble fraction of guinea pig brain is catalysed by four enzymes namely a pyroglutamate aminopeptidase, a post-proline cleaving enzyme, a post-proline dipeptidyl aminopeptidase and a proline dipeptidase. 1. The pyroglutamate aminopeptidase was purified to over 90% homogeneity with a purification factor of 2868-fold and a yield of 5.7%. In addition to catalysing the hydrolysis of thyroliberin, acid thyroliberin and pyroglutamate-7-amido-4-methylcoumarin the pyroglutamate aminopeptidase catalysed the hydrolysis of the peptide bond adjacent to the pyroglutamic acid due in luliberin, neurotensin, bombesin, bradykinin-potentiating peptide B, the anorexogenic peptide and the dipeptides pyroglutamyl alanine and pyroglutamyl valine. Pyroglutamyl proline and eledoisin were not hydrolysed. 2. The post-proline cleaving enzyme was purified to apparent electrophoretic horn hetty with a purification factor of 2298-fold and a yield of 10.6%. The post-proline cleaving enzyme catalysed the hydrolysis of thyroliberin and N-benzyloxycarbonyl-glycylproline-7-amido-4-methylcoumarin. It did not catalyse the hydrolysis of glycylproline7-amido-4-methylcoumarin or His-Pro-NH2. 3. The post-proline dipeptidyl aminopeptidase was partially purified with a purification factor of 301-fold and a yield of 8.9%. The post-proline dipeptidyl aminopeptidase catalysed the hydrolysis of His-Pro-NH2 and glycylproline-7-amido-4-methylcoumarin but did not exhibit any post-proline cleaving endopeptidase activity against thyroliberin or N-benzyloxycarbonyl-glycylproline-7-amido-4-methylcoumarin. 4. Studies with various functional reagents indicated thai the pyroglutamate aminopeptidase could be specifically inhibited by 2-iodoacetamide (100% inhibition at an inhibitor concentration of 5 μM), the post-proline cleaving enzyme by bacitracin (IC50 = 42 μM) and the post-proline dipeptidyl aminopeptidase by puromycin (IC50 = 46 μM). Because of their specific inhibitory effects these three reagents were key elements in the elucidation of the overall pathway for the metabolism of thyroliberin by guinea pig brain tissue enzymes. [ABSTRACT FROM AUTHOR]

1. Aminooxyacetate is a potent inhibitor of glutamate oxaloacetate transaminases from both rat and guinea pig kidney cortex. 2. In guinea pig kidney cortex, phosphoenolpyruvate carboxykinase activity was found to be 59% cytoplasmic, 41% mitochondrial. 3. Mitochondrial phosphoenolpyruvate carboxykinase activity is expressed only after sonication indicating that the enzyme is located within the inner mitochondrial membrane. 4. Aminooxyacetate inhibits gluconeogenesis from lactate, but not from pyruvate, in both rat and guinea-pig kidney cortex. 5. It is concluded that gluconeogenesis in guinea-pig kidney cortex proceeds by a pathway involving cytoplasmic, rather than mitochondrial phosphoenolpyruvate carboxykinase. [ABSTRACT FROM AUTHOR]