The effect of sulphydryl reagents on haemagglutinating encephalomyelitis virus (HEV), a coronavirus of pigs, was investigated. Using increasing concentrations of dithiothreitol (DTT), 50% of the virus infectivity and haemagglutination (HA) activity could be removed by 1.5 m and 4 to 5 m respectively. The effect of DTT concentrations on the polypeptide composition was also examined. Of the three external glycoproteins gp 125 was found to be the most susceptible, 50% being removed by incubation of the virus with 5 to 6 m-DTT. Of the other two glycoproteins gp 180 was unaffected by DTT concentrations up to 100 m and the amount of gp 100 gradually declined at concentrations above 20 m. The rates of removal of the virus HA activity and gp 125 suggested that this polypeptide was an essential part of the virus haemagglutinin. The lack of evidence for any interpeptide disulphide bonds suggested that the loss of these glycoproteins was due to an alteration in their conformation brought about by the cleavage of intrapeptide disulphide bonds. The loss of protein from the surface of the virus resulted in a change in the virus morphology with the appearance of thin fibrous projections instead of the characteristic petal-like coronavirus projections.


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