Enzymatic activities of cell-free extracts of Rickettsia typhi

Abstract

Cell-free extracts of R. typhi were tested for activities of enzymes of the tricarboxylic acid cycle, glutamate catabolism and glycolysis. The organisms were grown in the yolk sacs of chicken embryos, harvested shortly before the time of embryo death, purified by Renografin density gradient centrifugation, and ruptured in a French pressure cell. The following enzymatic activities were demonstrated: high levels of malate dehydrogenase (MDH); moderate levels of glutamate-oxaloacetate transaminase; glutamate, succinate and isocitrate dehydrogenases and citrate synthase; and low levels of glutamate-pyruvate transaminase. The specific activities of some of these enzymes were higher when the rickettsiae were harvested at a time of active proliferation, 3-4 days prior to embryo death. Rickettsial MDH was differentiated from host MDH by its migration pattern on polyacrylamide gel electrophoresis. The activities of MDH and 2 other dehydrogenases, demonstrable after the cells were disrupted, were absent from purified intact rickettsial preparations. No activity was detected for G-6-P, 6-phosphogluconate, glyceraldehyde-3-phosphate and lactate dehydrogenases, phosphoglucose isomerase, fructoaldolase, or pyruvate kinase. Apparently extracts of R. typhi that contain demonstrable enzymes involved in the catabolism of glutamate and tricarboxylic acid cycle intermediates, unlike Coxiella burnetii, lack detectable glycolytic activity.