Purines Staph, aureus

Fig. 20. Effect of the addition of a mixture of purines and pyrimidines on the rate of synthesis of protein in Staph, aureus incubated with a complete mixture of amino acids at different concentrations. (Gale and Folkes, 1953a.)...

Figure 22 also shows the effect of modifying the components of the purine-pyrimidine mixture in the presence of a complete amino acid mixture. Addition of any single purine or pyrimidine has little effect compared with the action of the complete mixture. Omission of single purines or pyrimidines, with the exceptions of uracil and xanthine, does not significantly decrease the nucleic acid synthesis omission of uracil decreases the synthesis to the level obtained with amino acids alone. This can be correlated with the finding that Staph, aureus is unable to syn-... 

Fig. 26. Progress curves for (a) nucleic acid synthesis and (b) protein synthesis in washed suspensions of Staph, aureus incubated with 1, glucose and a complete mixture of amino acids 2, as (1) - - complete mixture of purines and pyrimidines 3, as (2) + 30 Mg. chloramphenicol/ml. 4, glucose and mixture of purines and pyrimidines 5, as (4) -t- 30 Mg. chloramphenicol/ml. (Gale and Folkes, 1953b.)...

The addition of purines and pyrimidines accelerates the rate of protein synthesis in washed Staph, aureus as shown above. If penicillin in high concentrations is added to the incubation mixture, the additional protein synthesis due to the presence of purines and pyrimidines is abolished, although the basal protein synthesis is not significantly affected, as shown in Fig. 29. This effect is accompanied by a decrease in the purine-stimulated nucleic acid formation, but the concentration of penicillin which abolishes the additional protein synthesis does no more than halve (and frequently less than halve) the additional nucleic acid synthesis. Estimation of the proportions of the purine and pyrimidine bases in the nucleic acid fraction by the method of Smith and Markham (1950) modified by Wyatt (1951) shows that the changes lie in the ribonucleic acid fraction and that there is no significant alteration in the proportions of the various bases whether penicillin is present or not (Gale and Folkes, 1953b). 

Hotchkiss (1949) found that suspensions of Staph, aureus incubated with mixtures of amino acids, purines, and pyrimidines in the presence of penicillin took up more uracil than in the absence of penicillin. It is possible that there is a connection between these various investigations. Since there is no obvious alteration in the uracil content of the staphylococcal nucleic acid formed in the presence of penicillin (Gale and Folkes, 1953a Park, private communication) it seems that the formation of the uridine-5 -pyrophosphate derivatives may represent a stimulation of a side reaction rather than a side-tracking of the incorporation of uracil into nucleic acid. On the other hand, should the incorporation of an essential base into nucleic acid be inhibited, it is probable that the whole nucleic acid synthesis would cease rather than that the relative proportions of the bases within the nucleic acid should change. The true answer must probably await the development of a method for the study of nucleic acid synthesis in detail. George and Pandalai (1948) have claimed that the action of penicillin can be reversed by the addition of nucleic acid to cultures. 

Penicillin has no effect on protein synthesis by washed Staph, aureus under the author s experimental conditions until the concentration is raised to a value several orders above the hmiting bactericidal level. It does, however, prevent the increase in rate of protein synthesis that normally follows the addition of purines and pyrimidines to the external medium. Its action is therefore somewhat similar to that of bacitracin except that it does not inactivate the protein-synthesizing mechanism of the cell which is not synthesizing nucleic acid. For the present its action is indicated in Fig. 33 as a blocking of the pre-protein template concerned with nucleic acid synthesis but the high concentrations and partial effects obtained would suggest that, if it does act in this way, it affects a specific part of the template system rather than the whole mechanism. This will be elaborated below. 

Whether the CO was needed for purine synthesis or whether the purine played a part in producing CO, which was needed for growth, was not determined. With many bacteria, CO is essential at least for the initiation of growth (c/. 106). These observations should be compared with the relation between pyridoxin requirement and 0 tension observed by Boho-nos, Hutchings, and Peterson (15) (see Section IV, 3) and the uracil-0 effect found by Richardson with Staph, aureus (293). 

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