BIOCHEMISTRY OF INSECT VIRUSES 509 



When inclusion body proteins are dissolved, according to the standard 

 method for the liberation of virus particles (Bergold, 1947, 1957) in weak- 

 solutions of alkali (0.005 lf-0.03 M NaaCOg + 0.05 M NaCl for 1 to 3 hr.). 

 a yellow, almost clear solution of the inclusion body protein is obtained after 

 the sedimentation of virus particles at 10,000-12,000 g. In order to remove a 

 few remaining virus particles and virus membranes, the solution is ultra 

 centrifuged for 30 min. at about 25,000 g. The resulting clear solution repre- 

 sents the inclusion body protein, which can be precipitated by lowering the 

 pH with HCl or CH3COOH, or by dialysis against distilled water. The pre- 

 cipitate can be washed with slightly alkaline water and dissolved again in 

 dilute alkalis. When this process is repeated several times, one can obtain a 

 very pure preparation of inclusion body protein. Such protein solutions are, 

 under certain salt and pH conditions, very homogeneous and yield molecular 

 weights of about 276,000-378,000 (Bergold, 1947, 1948). Panebianco (1895) 

 claims to have recrystallized polyhedra by adding H2SO4, but all attempts 

 by the reviewer had no success, although some more or less regular patterns 

 are found when polyhedron protein solutions are allowed to dry. 



Apart from being insoluble in water, the inclusion body proteins behave 

 quite unusually. They are very sensitive to any salts; for instance, 0.01 M 

 NaCl at pH 8 causes aggregation and increases the sedimentation constant 

 from about 12.5 to 18.0 Svedberg (double molecules). The main molecule of 

 B. mori polyhedron protein, with a molecular weight of 378,000, dissociates 

 reversibly into its first spHt component with a molecular weight of about 

 60,500, or sixths (theoretically 63,000). Further addition of alkali causes the 

 sixths to split irreversibly into the second split component, or eighteenths, 

 with a molecular weight of 20,300 (theoretically 21,000) (Bergold, 1947). 

 In agreement with this finding, Kratky (1943, cited in Bergold, 1947) 

 found in small angle X-ray investigations a molecular weight of 22,000 

 for the smallest elementary cell, with dimensions of 45.3 X 28 X 20.4 A. The 

 second split component is not destroyed by boiling briefly in 0.5 M NaOH 

 and it crystallizes in bodies up to 5 /x in diameter and similar in appearance 

 to polyhedra (Glaser and Chapman, 1916; Bergold, 1947). It was recently 

 found that a major part of B. mori polyhedra (about 70 %) dissolves in 

 alcohol after pretreatment with trichloroacetic acid (Eto, 1956a, b). This 

 might be due to a partial degradation into the second split component 

 (18ths). Storage of B. mori polyhedra for thirty-seven years in a desiccator 

 over CaClg does not change their solubility in NagCOg (Aizawa, 1953, 1954). 



Undissolved B. mori polyhedra migrate in an electrical field to the positive 

 pole (von Prowazek, 1913; Dikasova, 1949) with an isoelectric point at 

 pH 5.2 (Tarasevich, 1945). Polyhedron protein solutions move homogeneously 

 but with different mobihties. They are completely insoluble at their isoelectric 

 points, which are at pH 5.7 for P. dispar and between pH 5.3 and 5.6 for 



