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The Quinine Inhibition of Bacterial Luminescence¹

The intensity of luminescence in non-proliferating, luminous bacteria suspended in phosphate-buffered salt solution is immediately decreased on addition of quinine. This inhibition is independent of cell concentration and is immediately reversible by diluting or by centrifuging and resuspending the cells in a medium without quinine.

An analysis of the relation between concentration and inhibition, at constant temperature and hydrostatic pressure, indicates that the average ratio of combining molecules is 1 to 1.5 for quinine and its site of action, respectively, in the equilibrium.

The relation of inhibition to temperature shows that it is dependent on the specific, normal, optimum temperature of the process in the organism concerned. In general, the inhibition increases as the temperature is raised towards and beyond the optimum. A given concentration of quinine, at a given temperature, may thus result in widely different potencies of effect according to the normal temperature-intensity relation of the luminescent oxidative reaction in different species. In the presence of the drug, the optimum is shifted to lower temperatures than normal.

Experiments with crude extracts of the luminescent luciferin-luciferase system of Cypridina show that the luminescent reaction may be directly affected by quinine. In bacteria, an analysis of the temperature data indicates that more than a single reaction is affected. In general, however, the type of action resembles that of urethane, alcohols, acetone, and similar inhibitors which promote reversible denaturation of the protein enzyme.

The quinine inhibition of bacterial luminescence is sensitive to hydrostatic pressure, which, under certain conditions, may completely abolish the effect of the drug.

Evidence for a combination of quinine with sulfanilamide and with butyl alcohol, predictable on theoretical considerations, was found in the mutual antagonism of the luminescence inhibition exhibited by mixtures of these of these drugs at favorable concentrations and temperatures. In general, the net result obtained with mixtures was either an antagonism or synergism, depending on the relative concentrations involved and the tendency of the drugs to combine with each other as well as with the catalytic systems in the cells.

Received February 7, 1944.
¹ This investigation was carried on in conjunction with a project at New York University concerning the action of the cinchona alkaloids, directed by Dr. Dugald Brown and aided by a grant from the Cinchona Products Institute Inc.