Crithidia luciliae: effect of purine starvation on S-adenosyl-L-methionine uptake and protein methylation.
The utilization of S-adenosyl-L-[methyl-3H]methionine ([3H-methyl]AdoMet) by Crithidia luciliae was assessed under nutrient-replete and purine-starvation conditions. Uptake experiments with intact cells demonstrated that the radiolabel from this molecule was accumulated by purine-starved organisms at a rate approximately 10-fold greater than that observed in those cultivated in nutrient-replete medium. Purine-starved cells also incorporated the radiolabel into trichloroacetic acid insoluble material at an approximately 10-fold faster rate than nutrient-replete cells. No differences, however, were observed in the intracellular levels of AdoMet and its metabolites between organisms cultivated under the two conditions. Results of comparative labeling studies with [3H-methyl]AdoMet, S-adenosyl-L-[carboxyl-14C]methionine, L-[methyl-3H]methionine and L-[35S]methionine in the presence and absence of cycloheximide demonstrated that the incorporation of label from [3H-methyl]AdoMet was due to transmethylation and was independent of protein synthesis. Further, approximately 15 methylated protein bands were identified by SDS-PAGE analysis. Lysates from both purine-starved and nutrient-replete organisms demonstrated similar levels of activity of three protein methyltransferases (PMI, II, III). The differences observed in [3H-methyl]AdoMet utilization between purine-starved and nutrient-replete C. luciliae may reflect the enhanced purine transport capacity which results from purine starvation.
Cell Biology Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892-0425, USA.
M M
MM
Alleman
V H
VH
Mann
C J
CJ
Bacchi
N
N
Yarlett
M
M
Gottlieb
D M
DM
Dwyer
D000241:Adenosine / Q000031:analogs & derivatives; D000818:Animals; D003421:Crithidia / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D003653:Decarboxylation; D008715:Methionine / Q000378:metabolism; D008745:Methylation; D011496:Protein Methyltransferases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011687:Purines / Q000378:metabolism*; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000031:analogs & derivatives / Q000378:metabolism*; D013872:Thionucleosides / Q000378:metabolism
D011500:Protein Synthesis Inhibitors; D011687:Purines; D013872:Thionucleosides; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D003513:Cycloheximide; D008715:Methionine; D011496:Protein Methyltransferases; D000241:Adenosine