Amino acids Staph, aureus

Park and Johnson found that three uridine nucleotides accumulated in Staph, aureus treated with penicillinii . The major nucleotide (LVIII) was later shown to consist of uridine 5 -pyrophosphate (UDP) linked to a new N-acetylamino sugar that is linked in turn to a peptide. The new amino sugar occurs in the cell walls of a number of bacteria and has been named muramic acid. It is an ether of D-glucosamine and lactic acid (GNAc-lactic)... 

Certain D-amino acids can be formed in bacteria by processes involving a racemase and D-amino acid transaminases. Amino acid activating systems have been found for D-alanine in Staph, aureus and a number of other bac-teria 34 is thus possible that free D-amino acids are sometimes incorporated as such into peptide antibiotics. On the other hand, the D-valine fragment of the penicillins arises from changes in an intermediate peptide that contains an L-valine residue. L-Valine in the culture fluid appears to be the precursor of the D-valine residue found in some of the actinomycins, but this relationship does not reveal the stage at which the inversion of configuration occurs. Differences in the permeability of cells or intracellular structures to l- and D-amino acids are liable to complicate the interpretation of experiments in this field. 

For net protein synthesis to occur in the animal body, it is necessary for the essential amino acids to be administered simultaneously for net protein synthesis to occur in suspensions of Staph, aureus, a complete amino acid mixture is required in the suspension medium, Gale and Folkes observed, however, that C Mabeled glutamic acid and phenylalanine were actively incorporated into the protein of Staph, aureus when other amino acids were absent and no increase in protein occurred. These authors point out that the inhibition of protein synthesis should affect the incorporation of all amino acids to the same extent. Actually it was observed that p-chlorophenylalanine inhibited protein synthesis and the incorporation of phenylalanine almost completely without significantly reducing the incorporation of glutamic acid. The inhibition by p-chloro-phenylalanine was strictly competitive. Study of the action of antibiotics, which also inhibit protein synthesis, revealed that the incorporation of phenylalanine was more sensitive to inhibition by chloramphenicol and aureomycin than was glutamic acid, whereas the converse was true... 

The accumulation of lysine within Strep, faecalis and Staph, aureus takes place as a result of diffusion of the amino acid through the surface structures of the cells. Taylor (1949) found that lysine was concentrated to a high degree by yeasts, but with these organisms no accumulation of lysine took place unless a source of energy such as glucose was available. 

Inhibition by Other Amino Adds. Gale and Van Halteren (1951) found that the rate at which suspensions of Staph, aureus accumulate glutamic acid is affected by the presence of other amino acids when these are added singly to the incubation mixture. Table VII shows that the... 

An indication of the part played by active processes in the accumulation of a variety of radioactive amino acids by Staph, aureus has been obtained by the author (Gale, 1953) in the following way. Washed suspensions of cells were incubated with glucose and a suitable concentration of a randomly labeled amino acid in the presence and absence of 0.01 M 2,4-dinitrophenol after equilibration, the radioactivity per unit volume of the supernatant medium and of the cell contents (liberated by treatment with CTAB) was determined. Since the radioactivity measurements were not specific, the activity of the cell contents included that of any breakdown products of the amino acid used but the ratio of internal to external radioactivities gave a measure of the concentration achieved across the cell wall, while the effect upon this ratio of the presence of dinitrophenol (DNP) showed the extent to which active transfer processes played a part in that concentration process. Results are shown in Table XI. 

If washed cells of Staph, aureus are incubated with glucose and a complete mixture of amino acids, their protein content increases by as much... 

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.)...

Fig. 21. Progress curves for the incorporation of C Mabeled glutamic acid into the cell protein of Staph, aureus when incubation takes place in the presence of glucose and (a) glutamic acid only, (b) a complete mixture of amino acids including glutamic acid. (Gale and Folkes, 1953c.)...

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.)...

Fia. 27. Inhibitory actions of aureomycin on stages of assimilation of amino acids in Staph, aureus. Key as for Fig. 25. (Gale and Folkes, 1953b,c.)... 

Fig. 28. Inhibitory actions of neomycin on glutamic acid incorporation in Staph, aureus incubated with glucose and (1) glutamic acid only, (2) complete amino acid mixture. Cross-hatched area indicates growth-inhibitory range of concentration.

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