STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 95 



Rickenberg, 1957). Indeed, a recent report indicates the most rapid incor- 

 poration of labeled glycine occurs in the protein of the protoplast membrane 

 (Hunter et al., 1957). 



Thus, in these forms at least, the activation of amino acids prior to later 

 assembly stages does not occur 'at the cell waE. As \^^U be noted below, a 

 considerable degree of synthesis of ceU waU peptides is accomplished within 

 the cell prior to final assembly into cell wall, 



{h) Effect of Ribonudease. If fertilized amphibian eggs are injected with 

 pancreatic ribonudease, mitosis is inhibited (Thomas et al., 1946; Ledoux 

 et al., 1954). This inhibition is not obtained with DNAase, trypsin, or pepsin. 

 Ribonudease has also been observed to inhibit amino acid incorporation by 

 protoplasts (Lester, 1953), bacteria degraded by ultrasonic waves (Gale and 

 Folkes, 1954), and by microsomal preparations (Allfrey ^i al., 1953; Zamecnik 

 and Keller, 1954; Hultin et al, 1957). 



When this enzyme is added to intact plant and animal cells, various effects 

 have been noted on basophilia, cell permeability, and mitosis (Lansing and 

 Rosenthal, 1952; Kaufmann and Das, 1954), suggesting that the enzyme of 

 molecular weight 13,000 can penetrate the ceU membrane of many kinds of 

 cells quite readiJy. These results were readily confirmed and extended 

 (Ledoux et al., 1954), and the effects were shown not to be produced by basic 

 proteins in general. However, Brachet (1956) considers that the enzyme 

 works in two ways on onion root tips; a ribonudease complex is formed first 

 with intracellular RNA and the RNA is subsequently degraded. Relatively 

 enormous amounts of enzyme can be taken into treated cells, perhaps by 

 pinocytosis. 



As summarized by Brachet (1955b), onion roots, frog eggs, starfish oocytes 

 are moderately sensitive to the enzyme; amoebae and ascites tumor cells 

 are very readily attacked. A number of cell types, e.g., Acetabularia, fungi, 

 yeasts, and ciliates, which possess tough cell walls, seem impermeable. 

 Although bacteria such as E. coli at first seemed resistant to the enzyme, 

 RNAase can penetrate at sufficiently low ionic strength (Jerne and Maal^ie, 

 1957). In the hands of these workers, it could be shown that the application 

 of RNAase to E. coli reduces the RNA content, stops protein synthesis, and 

 kills the bacterium. If the bacteria had been uifected with virus, e.g., T4, 

 the plaque-forming abiMties of the complex were also destroyed after a 

 4-minute exposure to the enzyme. 



Treatment of onion roots with RNAase produces a marked inhibition of 

 incorporation of labeled amino acids and of growth, which is reheved by the 

 addition of RNA. The enzyme affects ATP concentration, producing an 

 initial rise and then a fall, but does not affect Og consumption. 



Ledoux and his collaborators (Ledoux and ReveU, 1955; Ledoux, 1956; 

 Easty et al., 1956) have studied the effect of the enzyme on neoplastic growth. 



VOL. I — 8 



