Arginase in lactating bovine mammary glands: implications in proline synthesis

Journal of Dairy Science
J J BaschH M Farrell

Abstract

The occurrence and subcellular distribution of arginase have been studied in mammary glands from lactating dairy cattle. The enzyme appears to be localized in the mitochondrial fraction, although a significant amount has been found to be associated with the cytosolic fraction. Both mitochondrial and cytosolic arginase are activated by heating with Mn2+. The Michaelis constants for the two fractions, however, are different: 49.5 and 18.5 mM for the mitochondrial fraction and cytosolic fraction, respectively. Overall the total enzyme concentration in the gland suggests that these enzymes contribute to the conversion of arginine to ornithine. Ornithine, in turn, may be converted by ornithine aminotransferase into an intermediate, L-delta 1-pyrroline-5-carboxylate; concurrently. alpha-keto-glutarate is transformed into glutamic acid. Finally, pyrroline-5-carboxylate reductase yields proline, an important amino acid that is needed for casein synthesis. Because pyrroline-5-carboxylate reductase requires NADPH, and because ornithine aminotransferase uses alpha-ketoglutarate, this new pathway is linked to the Krebs cycle through the cytosolic isocitrate dehydrogenase, which is the source of both of these intermediates.

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Citations

Nov 9, 2000·Proceedings of the National Academy of Sciences of the United States of America·S A Maxwell, G E Davis
Sep 10, 2014·Amino Acids·Rodrigo ManjarinNathalie L Trottier
Sep 22, 2010·Journal of Basic and Clinical Physiology and Pharmacology·Ljiljana BjelakovićGordana Bjelaković

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