CHARACTERIZATION OF A RIBOSOME-LINKED GUANOSINE TRIPHOSPHATASE IN ESCHERICHIA COLI EXTRACTS

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Abstract
The close overlap of amino-acid incorporation and guanosine triphosphatase (GTPase) activity with the polyuridine (U)-ribosome fraction suggests that a GTP split is associated with protein synthesis. A guanosine diphosphate (GDP) inhibition of GTPase and polypeptide synthesis indicates the correlation. Nevertheless, a relatively weak response to change in ionic development but not a dependence on sRNA makes the parallel incomplete. The destruction of the polymerization function by heating to 55[degree] stimulates GTP hydrolysis. This may be interpreted as an uncoupling of a functional transfer of the terminal phosphoryl of GTP. The energy of the peptidyl rather than the aminoacyl link to sRNA mostly forms new peptide bonds. By removing the influence of 8407 [1965] PHYSIOLOGY AND BIOCHEMISTRY OF BACTERIA 103825-103834 the amino-group from the ester link, the group potential of peptidyl sRNA may be substantially lower than that of aminoacyl sRNA, as indicated by the decrease in sensitivity to alkali. Quite a different energy requirement for a forward move of messenger RNA on the ribosomes parallel to the extending peptide chain may be postulated. After every peptide bonding to a new aminoacyl sRNA, the lengthened peptidyl sRNA slides from acceptor site to donor site and pulls the messenger RNA 1 notch ahead at the same time. This movement is repeated every time a peptide bond is formed; it could be coincidental with an alternate contraction and expansion of the ribosome dependent on GTP split. The GTPase function requires the assembly of the 50S and 30S particles into the whole ribosome, this possibly indicating interaction between the aminoacyl sRNA on the 50S and messenger RNA on the 30S parts. The association of GTPase with one of their separable aminoacyl sRNA transfer enzymes from rabbit reticulocytes was reported. This fraction + GTP promotes a poly U-dependent binding of phenylalanyl sRNA to ribosomes. The extensive hydrolysis of GTP was interpreted as being due to the constant synthesis, breakdown and resynthesis of an extremely labile intermediate. The close interrelationship between GTP split and amino-acid polymerization favors (but does not prove) that a phosphoryl split is connected with some phase in protein synthesis.

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