title: Characterization of the elongation factors from calf brain. 3. Properties of the GTPase activity of EF-1 alpha and mode of action of kirromycin.
abstract: The GTPase activity of purified EF-1 alpha from calf brain has been studied under various experimental conditions and compared with that of EF-Tu. EF-1 alpha displays a much higher GTPase turnover than EF-Tu in the absence of aminoacyl-tRNA (aa-tRNA) and ribosomes (intrinsic GTPase activity); this is due to the higher exchange rate between bound GDP and free GTP. Also the intrinsic GTPase of EF-1 alpha is enhanced by increasing the concentration of monovalent cations, K+ being more effective than NH+4. Differently from EF-Tu, aa-tRNA is much more active than ribosomes in stimulating the EF-1 alpha GTPase activity. However, ribosomes strongly reinforce the aa-tRNA effect. In the absence of aa-tRNA the rate-limiting step of the GTPase turnover appears to be the hydrolysis of GTP, whereas in its presence the GDP/GTP exchange reaction becomes rate-limiting, since addition of EF-1 beta enhances turnover GTPase activity. Kirromycin moderately inhibits the intrinsic GTPase of EF-1 alpha; this effect turns into stimulation when aa-tRNA is present. Addition of ribosomes abolishes any kirromycin effect. The inability of kirromycin to affect the EF-1 alpha/guanine-nucleotide interaction in the presence of ribosomes shows that, differently from EF-Tu, the EF-1 alpha X GDP/GTP exchange reaction takes place on the ribosome.
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002417:Cattle; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008024:Ligands; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011072:Poly U / Q000494:pharmacology; D011728:Pyridones / Q000494:pharmacology; D012333:RNA, Messenger / Q000494:pharmacology; D012346:RNA, Transfer, Amino Acyl / Q000494:pharmacology; D012270:Ribosomes / Q000378:metabolism
chemical_list: D008024:Ligands; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors; D011728:Pyridones; D012333:RNA, Messenger; D012346:RNA, Transfer, Amino Acyl; D006153:Guanosine Diphosphate; D011072:Poly U; D006160:Guanosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D020963:GTP Phosphohydrolase-Linked Elongation Factors; C008536:mocimycin