SUMMARY: When concentrated by precipitation with acid and salts, or by highspeed centrifugation, potato virus tends to become insoluble though still remaining infective and serologically active. This greatly complicates purification and no method was found that could be relied upon to give good yields of virus with constant properties. Insolubility is correlated with the aggregation of virus particles to form long threads that become entangled, but it is probable that combination of the particles with some cell constituents is also concerned.

Insoluble preparations dissolve slowly when incubated with pH 7.5 borate buffer, and rapidly in the presence of trypsin or chymotrypsin. Both of these enzymes hydrolyse virus , chymotrypsin being the more effective, but different strains of the virus vary in their susceptibility.

Ribonuclease readily hydrolyses the nucleic acid derived from virus , but seems to have no enzymic action on the active virus. When mixed with the virus, the enzyme combines with it and reversibly inhibits infectivity. At pH 7 the addition of ribonuclease to soluble virus preparations causes loss of anisotropy of flow, a fall in precipitin titre, and the production of an insoluble complex. Incubation at pH 7.5 with borate buffer slowly dissolves the complex and restores the original properties of the virus; the rate of re-solution is increased by the presence of trypsin. Some preparations of the virus were partially decomposed by incubation with borate buffer, and sometimes the rate of decomposition was increased in the presence of ribonuclease.


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