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.
Alleman
M M
MM
Cell Biology Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892-0425, USA.
Mann
V H
VH
Bacchi
C J
CJ
Yarlett
N
N
Gottlieb
M
M
Dwyer
D M
DM
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