[Various physical and chemical properties of the 73s unit of the foot-and-mouth disease virus].

At all 3 studied FMD-viruses typs O2, A5 and C we could show the 73S unit in the analytical ultracentrifuge and in the electron microscope. 73S unit is found in the normal cycle of purification of virus and by density gradient centrifugation separated and purified. In CsCl pH 7.6 its density is 1.308 +/- 0,005 g/ml. Its sedimentation coefficient has a value of 72.7 +/- 1,5S. In electron microscope it show itself as a empty virus capsid. Its diameter is in partial purified preparations with 25 +/- 1 nm the same as of the virion. Its wall diameter is 2 to 3 nm. Further purification induced defiguration of particles and increase of its diameter. 73S unit dissociates in 19S and 12S units and shows a typical protein-UV-absorption spectrum with a maximum at 276 to 278 nm and a minimum at 250 nm. Emax/Emin is 2.3. Extinction coefficient E276nm is 1,4 mg/cm2. By sucrose density gradient centrifugation and titration of fractions in the complement fixation test it was detected, that croude virus solution contained already the 73S unit.