Six strains of Rickettsia prowazekii, two derived from human infections and four isolated from flying squirrels, two strains of R. typhi, and the single available strain of R. canada, were characterized by several biochemical procedures. The electrophoretic patterns on polyacrylamide gels of rickettsial proteins solubilized by sodium dodecyl sulfate revealed several species differences, but strains of the same species appeared to have identical patterns. Cytoplasmic fractions of the rickettsiae were examined for enzymatic activities and for polyacrylamide gel isoelectric focusing patterns. Some species differences were encountered in the activities or ratios of activities of glutamate-oxaloacetate transaminase, glutamate dehydrogenase, and malate dehydrogenase. When polyacrylamide gels were stained for malate dehydrogenase after electrophoresis, a single band became apparent with single extracts or mixtures of two strains of R. prowazekii, but two bands were seen with mixtures of a strain of R. prowazekii and one of R.

Species-specific antigens from Rickettsia typhi and Rickettsia prowazekii were readily solubilized by French pressure cell extraction or sonication of Renografin density gradient-purified rickettsiae and were identified by rocket immunoelectrophoresis. As measured by quantitative rocket immunoelectrophoresis, the species-specific typhus rocket antigens (STRAs) appeared to be proteins; they were denatured by heating at 560C for 30 min but not by 50°C treatment, and they were sensitive to pronase and trypsin but were not affected by periodate oxidation, glycosidases of various specificities, phospholipase A, or lipase. STRAs from both R. typhi and R. prowazekii were separated from common antigens by DE52 column chromatography of 100,000-x-g supernatant fractions of rickettsial extracts. The purified STRAs were characterized by crossed immunoelectrophoresis, by polyacrylamide gel electrophoresis on Davis and sodium dodecyl sulfate gels, and by an enzyme-linked immunosorbent assay. The two purified STRAs were proteins with similar native electrophoretic mobilities in agarose and polyacrylamide gels, and these proteins had similar polypeptide pattems on sodium dodecyl sulfate gels. Most of the STRA activity migrated as a single protein band on sodium dodecyl sulfate-polyacrylamide and Davis polyacrylamide gels, although minor protein bands with STRA activity were also detected. The major STRA proteins constituted 10 to 15% of the total cellular protein of R. typhi and R. prowazekii. According to sensitive enzyme-linked immunosorbent assay titrations, the STRA of R. prowazekii had substantial cross-reactivity with rabbit antiserum prepared against R. typhi, as shown also by rocket immunoelectrophoresis, whereas the STRA of R. typhi reacted only very weakly with antiserum prepared against R. prowazekii according to the enzyme-linked immunosorbent assay and not at all according to rocket immunoelectrophoresis.