364 KICHARD SCHWEKT AND JOHN BLSHOP 



protein synthesis has been demonstrated (see discussion of membrane 

 protein synthesis below). Amino acyl-RNA compounds were shown to be 

 obligatoiy intermediates for hemoglobin synthesis in a cell-free system 

 (Allen and Sclnveet, 1960). 



2. The Transfer Reaction 



The transfer of amino acids from amino acyl-RNA to ribosomes has 

 now been observed in cell-free systems derived from a number of differ- 

 ent sources. J\Iany workers have employed the livers of noniial (Hoag- 

 land et al., 1958; Nathans and Hiilsman, 1960; jMoldave and Grossi, 

 1960; Takanami, 1961) or hepatectomized (von der Decken and Hultin, 

 1960) rats. Systems from rabbit reticulocytes (Bishop et al., 1960a; 

 von Ehrenstein and Lipmann, 1961), from E. coli (Nathans and Lip- 

 mann. 1961), and from pea seedlings (Webster, 1960) have also been 

 described. The i)henomcnon, then, appears to be quite general. 



a. Cofactorial Requirements for Transfer. A requirement for GTP in 

 the transfer process was first pointed out by Hoagland et al. (1958) and 

 has since been confirmed in a number of laboratories (Moldave and 

 Grossi, 1960; Nathans and Hiilsman, 1960; Bishop et al., 1960a; Nathans 

 and Lipmann, 1960; von Ehrenstein and Lipmann, 1961). In the reticulo- 

 cyte system, a maximum rate of transfer is observed in the presence of 

 GTP as the sole phosphorylated nucleoside (Schweet et al., 1961). Taka- 

 nami (1961) has succeeded in purifying a liver system to the extent that 

 ATP is inactive when it is the sole phosphorylated nucleoside present, 

 while GTP alone is active. Some workers (Hoagland et al., 1958; Grossi 

 and Moldave. 1960) have observed a requirement for ATP in addition 

 to GTP. Magnesium ion is reported to be required in the pea seedling 

 system (Webster, 1960), in rat liver systems (von der Decken and 

 Hultin, 1960; Takanami, 1961), and at a high level in the E. coli system 

 (Nathans and Lipmann, 1961). 



A requirement for glutathione, or other sulfhydryl compounds, has 

 been demonstrated (Nathans and Hiilsman, 1960; Hiilsman and Lip- 

 mann, 1960) in a rat liver system. In pea seedlings, the glutathione 

 requirement was absolute, and irreplaceable by other sulfhydiyl com- 

 pounds (Webster, 1960) ; but in E. coli the glutathione requirement 

 was less marked than in rat liver (Nathans and Lipmann, 1961). Again 

 in a rat liver system, however, Hirokawa et al. (1961) found little 

 requirement for glutathione, presumably because they used an undialyzed 

 pH 5 supernatant (see Hiilsman and Lipmann, 1960). More diflficult to 

 understand is the inhibitoiy effect of glutathione observed by Taka- 

 nami (1961) in a purified rat liver system. However, the purity of 

 commercial glutathione preparations is not always good, and Hiilsman 



