Derepression of nitrogenase in Azotobacter

When nitrogenase in $\text{Azotobacter vinelandii}$ 12837 is repressed by ammonia, the derepression is accelerated by endotoxin or cyclic AMP. The phenomenon appears neither to be a consequence of accelerated ammonia utilization nor altered activity of preformed enzyme. This is a unique example of an effect of endotoxin on a procaryotic system.     

ENZYME ASSOCIATED WITH BACTERIOPHAGE INFECTION.

Eklund, Curtis (The University of Texas, Austin) and Orville Wyss. Enzyme associated with bacteriophage infection. J. Bacteriol. 84:1209-1215. 1962.-A capsule-digesting enzyme was formed when azotobacter cells were infected with bacteriophage. The enzyme appeared in the medium when the phages lysed the cells. By disrupting phage-infected cells prematurely, it was shown that enzyme formation in the bacterium began shortly after invasion. The amount of enzyme formed was far in excess of that incorporated into the new phages. The enzyme was concentrated from the lysate, and its activity was measured under a variety of conditions.     

Purine and pyrimidine salvage in a clonal Drosophila cell line

A new culture medium, ZH1%, for Drosophila cell lines is described in which treatment of cells with the folate antagonist methotrexate (MTX) leads to overt double auxotrophy for both purines and pyrimidines. Using this medium the response of a clonal Drosophila cell line, KcAlo, to various purines and pyrimidines was measured. Guanosine was found to balance the toxicity of adenosine (AR), and vice versa. In addition AR toxicity was shown to be strongly dependent on the pH of the culture medium. Using ZH1% supplemented with MTX + thymidine (TdR) or with MTX + inosine (HR) several purines or pyrimidines, respectively, were tested for their capacity to support cell proliferation. This provided evidence for pathways for the salvage of thymine, TdR, thymidylic acid, adenine (A), AR, and HR. Bromodeoxyuridine and fluorodeoxyuridine are very active and specific TdR analogues inhibiting Drosophila cell proliferation. Of the many purine analogues tested the only potent growth inhibitor with demonstrable pathway specificity (antagonizable by A only) was methylpurine.