Nucleic Acids and Amino Acid Incorporation 175 



Disrupted Staphylococcal Cell Preparation 



If a suspension of Staphylococcus aureus is incubated in the 

 presence of glucose and a single amino acid, such as glutamic 

 acid, labelled with ^^C, the protein of the preparation acquires 

 radioactivity. This radioactivity is not removed by pro- 

 longed washing of the protein fraction with trichloracetic 

 acid, acetic acid, alkali, alcohol, ether or acetone and can be 

 released from the protein fraction only by such chemical 

 measures as result in hydrolysis of the peptide bonds. If the 

 amino acid in the incubation medium is glutamic acid, hydro- 

 lysis and separation of the protein residues after incubation 

 show that the radioactivity is confined to the glutamic acid 

 residues. Treatment of the protein with ninhydrin or by 

 application of Sanger's method for N-terminal groups (Sanger, 

 1945) shows that less than 3 per cent of the incorporated 

 residues occur as end-groups. It seems that the situation is 

 essentially similar to that studied by Borsook and his col- 

 leagues (reviewed by Borsook, 1954) in other tissues, and that 

 the incorporated radioactive amino acid has become part of 

 the structure of certain proteins of the preparation. 



If cells rendered radioactive, by incubation with glucose 

 and a labelled amino acid, are disintegrated by exposure to 

 supersonic vibration and the disintegrated material then 

 separated on the centrifuge into four fractions: (a) material 

 sedimented in 10 minutes at 800 g, (b) material sedimented in 

 20 minutes at 4000 g; (c) material sedimented in 60 minutes 

 at 16,000 g, and (d) "soluble" material, it is found that 

 Fraction (b) has the highest specific activity. Furthermore, 

 if freshly harvested cells are suspended in a buffered salt 

 solution containing 10 per cent sucrose, disintegrated, frac- 

 tionated in the same fashion, and the various fractions in- 

 cubated with ^^C-glutamic acid or glycine, together with 

 ATP as energy source, it is found that Fraction (b) is able 

 to incorporate the labelled amino acid rapidly, having 

 markedly greater activity than (a) while the activity of (c) 

 and (d) is negligible. Electron microscope examination of 



