This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Laliberté, G. Articles by Hellebust, J. A. Search for Related Content PubMed PubMed Citation Articles by Laliberté, G. Articles by Hellebust, J. A. Agricola Articles by Laliberté, G. Articles by Hellebust, J. A.

Metabolism and Enzymology

Partial Characterization of Ornithine Carbamoyltransferase in Three Microalgae ¹

Anabolic Role Only

Earth Sciences Centre, Department of Botany, University of Toronto, Toronto, Ontario, Canada, M5S 3B2

Although the existence of isozymes of ornithine carbamoyltransferase (carbamoylphosphate:L-ornithine carbamoyltransferase, EC 2.1.3.3) in higher plants has been reported, and the possibility exists that one or more of these operates catabolically to produce ornithine and carbamoylphosphate from citrulline and inorganic phosphate, no proof has been forthcoming. In view of the fact that many unicellular algae degrade arginine via arginine deiminase to citrulline and ammonium, and that the pathway of utilization of citrulline is unknown, we decided to investigate the possibility of the presence of a catabolic form of ornithine carbamoyltransferase in three microalgae known to have arginine deiminase activity. These were Chlorella autotrophica, Chlorella saccharophila, and Dunaliella tertiolecta. Our results show that the properties of OCT from these three algae are similar to OCTs from many higher plants with respect to general kinetics (K_m values for ornithine and carbamoylphosphate), substrate inhibition by ornithine at high pHs, apparent sequential ordered kinetic mechanisms and paucity of apparent regulatory properties. Our data indicate an exclusively anabolic role of ornithine carbamoyltransferase in these algae.