Isolation and partial characterization of the M(r) 100 kD protein from Rickettsia prowazekii strains of different virulence.

The major M(r) 100 kD protein (protein I) from the standard virulent R. prowazekii strain Breinl, from the nonvirulent strain E and its virulent revertant EVir were isolated by chromatography and characterized. Purified protein I from the three strains of different virulence and origin had the same physico-chemical and antigenic properties, protected guinea pigs against infection with the virulent strain Breinl and induced the production of antibodies, which neutralized the toxic and haemolytic activities of R. prowazekii. The amino acid composition of protein I as determined for the three above mentioned strains was similar. Modified residues of Lys, Asn, and/or Gln were found in protein I. Protein I from virulent strains Breinl and EVir differed from that of nonpathogenic strain E by the quantity of N epsilon-Me-Lys and N epsilon-Me3-Lys, but all had the same total amount of Lys and its derivatives. It may be suggested that a difference may exist in the processing of the protein I of nonpathogenic strain E and of virulent strains of R. prowazekii.