Virus of Avian Myeloblastosis. XVIII. Fixation of Myeloblasts and Phosphatase Activity of Loci of Virus Synthesis (Viroplasts)2

Abstract

Further work is reported on the phosphatase activity of the intracellular bodies (viroplasts) of myeloblasts from tissue cultures established with the primitive cells from the circulating blood of chickens diseased with avian myeloblastosis virus. Evidence obtained earlier indicated that the viroplasts are the specific sites of the synthesis of myeloblastosis virus, and that the viroplasts may be derived by virus infection of the precursors of granules developing in maturation of the myeloblast normally through the granulocytic series of white blood cells. Previous studies revealed that viroplasts and granules of normal myelocytes exhibited strong activity to dephosphorylate adenosine triphosphate. The present study shows that a parallel reaction occurred with both normal granules and viroplasts when inosine triphosphate was used as substrate in the Wachstein-Meisel procedure. Analogous tests with adenosine and inosine diphosphates gave slightly less pronounced reactions with granules of myelocytes, but those seen with the viroplasts were indistinguishable from results obtained with the triphosphates. Studies with adenylic acid, glucose-6-phosphate, and glycerophosphate, and tests for acid and alkaline phosphatase were entirely negative with both normal granules and viroplasts. Myeloblasts grown in culture medium containing 5-methyl tryptophan developed many large viroplasts concurrent with inhibition of cell growth, and did not lessen the rate of virus liberation by the cells. These viroplasts exhibited typical adenosinetriphosphatase activity. Methods for fixation of myeloblasts were improved by development of a practical sequence of quenching in liquid nitrogen, dehydration in vacuo at low temperatures, and fixation with formaldehyde vapor by which structural artifacts related to subsequent treatment can be controlled.