Polyamine biosynthesis in Phytomonas Biochemical characterization of a very unstable ornithine decarboxylase

MARCORA MS; CEJAS S; GONZÁLEZ NS; ALGRANATI ID; CARRILLO C

INTERNATIONAL JOURNAL FOR PARASITOLOGY

ELSEVIER SCI LTD

Año: 2010 p. 15 - 18

0020-7519

The metabolism of polyamines as well as their functions as growth regulators inplants have been extensively studied for many years. However, almost nothing isknown about the biosynthesis and roles of these substances in Phytomonas spp.,parasites of several plants. We have used HPLC and electrophoretic analyses toinvestigate the presence and metabolism of polyamines in Phytomonas Jma strain,detecting both putrescine and spermidine but not spermine. Experiments carriedout by incubation of intact parasites with labelled ornithine or putrescineshowed the formation of radioactive putrescine or spermidine, respectively. Theseresults indicated that Phytomonas Jma can synthesise these polyamines through theaction of ornithine decarboxylase (ODC) and spermidine synthase. On the otherhand, we could not detect the conversion of arginine to agmatine, suggesting the absence of arginine decarboxylase (ADC) in Phytomonas. However, we cannot ensure the complete absence of this enzymatic activity in the parasite. Phytomonas ODCrequired pyridoxal 5´-phosphate for maximum activity and was specificallyinhibited by alpha-difluoromethylornithine. The metabolic turnover of the enzyme was very high, with a half-life of 10-15min, one of the shortest found among all ODC enzymes studied to date. The parasite proteasome seems to be involved indegradation of the enzyme, since Phytomonas ODC can be markedly stabilized byMG-132, a well known proteasome inhibitor. The addition of polyamines toPhytomonas cultures did not decrease ODC activity, strongly suggesting thepossible absence of antizyme in this parasite. Copyright © 2010 AustralianSociety for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.