Transport of B-Vitamins in Microorganisms. V. Comparative Studies on the ATP-hydrolyzing Activities of Cell Fractions Obtained from Thiamine Sufficient and Thiamine Deficient Cells of L. fermenti.

Abstract

Normal and thiamine deficient cells of Lactobacillus fermenti were disrupted in a French press and subjected to differential centrifugation. The ATP-hydrolyzing activities of the resulting soluble and particulate fractions were studied. The cell fractions from both kinds of cells contain an adenosine triphosphatase which removes the terminal phosphate group from ATP. The enzyme requires Mg2+ for its activity, the optimum Mg2+: ATP ratio being close to 1:2. Ca2+ also activates the enzyme(s), although less efficiently than Mg2+; in the presence of Mg2+; however, Ca2+ ions are inhibitory. The Mg2+-activated ATPase is further stimulated in the presence of certain concentrations of Na+ and K+. In addition to the ATPase(s), the cell material also contains a pyrophosphatase which is found mainly in the soluble fraction. A comparison of the specific ATPase activities of a number of preparations obtained from normal and thiamine deficient cells indicates that the ATPase activity of cell fractions is depressed and the distribution of this activity between the particulate and soluble cell fraction is changed in favour of the soluble enzyme when the cells of L. fermenti are grown under conditions of thiamine deficiency.