Proline from ornithine catabolism

The inherited enzyme deficiencies listed in Table 11.2 lead to the accumulation of substrates and deficiencies of products. For correct interpretation of laboratory results, one need be aware that substrate accumulation can affect the prior enzyme in the pathway (e.g. increased carbamyl phosphate inhibits CPS). A deficiency of urea cycle intermediates (transport or enzyme products or dietary substances) e.g. arginine or ornithine, is often rate limiting. It can initiate a vicious cycle, which worsens the urea synthetic capacity in the cytosol (e.g. by limiting protein synthesis), or in the mitochondria (deficient stimulation of NAGS and of substrate for OTC). Measured plasma values reflect cytosolic metabolite concentrations, not those of mitochondria. Protein catabolism contributes to the plasma amino acid values. Thus, the interpretation of results for plasma arginine, proline and lysine must be done within the context of the pattern found for all of the amino acids. Urea concentrations depend upon the arginine in the cytosol originating from protein catabolism, urea cycle synthesis, and therapeutic applications. 

OAV is primarily derived from catabolic ornithine and is reduced to proline. 

Three of the amino acids, alanine, aspartic acid, and glutamic acid are readily formed by transamination from products of the citric acid cycle. This has been explained in the chapter. Carbon Catabolism of Amino Acids. Glutamic acid is the probable precursor of a considerable number of the other nonessential amino acids, namely, proline, hydroxy-proline, ornithine, and from it arginine. 

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