SUMMARY: Four analogues of pteroic acid and one of pteroylglutamic acid were tested for their ability to stimulate growth of Streptococmfaecalis R in the absence of pteroic acid or to inhibit growth in its presence. The four analogues of pteroic acid were inactive in either respect, but 2-deamhopteroylglutamk acid was inhibitory. Inhibition of the or anism wasmost marked in the presence of pteroic acid, and became relatively more efficient as the concentrations of inhibitor and growth factor were increased. Inhibition was much less marked in the presence of rhizopterin or Leucovorin, the relative efficiency decreasing in comparable conditions. Pteroylglutamic acid had an intermediate position and showed a competitive relationship.

Lactobacillus cmei was similarly inhibited when growth was supported by either pteroylglutamic acid or Leucovorin, but was less pronounced in the presence of the latter. On the other hand, the analogue could substitute for pteroylglutamic acid in stimulating the suboptimal growth supported by a mixture of thymine and a purine in the absence of added folic acid.

Several other organisms whose growth is independent of exogenous folic acid were unaffected by the analogue.


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