Functional identity of the monomeric and multiple forms of elongation-factor 1 from Krebs-II mouse ascites-tumor cells.

Highly purified 3H-labelled elongation factor 1 (EF-1) from Krebs II mouse ascites tumour cells was separated into biologically active monomeric and aggregate forms of the enzyme by either gradient centrifugation or gel filtration. When corrected for their content of inactive enzyme both forms of the factor were found to be equally active whether tested in the binding or synthesis reaction. The only form of the enzyme found bound to ribosomes was the monomer; it was therefore concluded that the aggregate form of the enzyme must first dissociate before it reacts with the ribosome. The stoichiometry of the aminoacyl-tRNA binding reaction to ribosomes in the presence of guanosine nucleotides was also studied. It was found that one molecule of aminoacyl-tRNA and of Guo-5'-P2-CH2-P is bound per molecule of EF-1 bound to the ribosome. Following interaction with a release from, the ribosomes, EF-1 was found to be predominantly monomeric.