Evidence for guanylate cyclase activity associated with hemagglutinating virus of Japan (Sendai virus)

Purified virions of HVJ (Sendai virus) were found to contain a guanylate cyclase activity that converts GTP to cyclic GMP. Activities of adenylate cyclase and 5'-nucleotidase which are frequently used as marker enzymes of cell membranes were not detected in the virus. Guanylate cyclase and virion-associated activities, neuraminidase and hemagglutinin, were co-purified during a purification of virions. Guanylate cyclase activity was not detected without disruption of the virions with a detergent, Triton X-100 or Nonident P-40. Treatment of intact HVJ with a proteolytic enzyme, trypsin or chymotrypsin, destroyed both neuraminidase and hemagglutinin; however, most of the guanylate cyclase ws retained. Guanylate cyclase activity was found in fractions containing nucleocapsids after sucrose density gradient centrifugation of disrupted virions. These results indicated that the enzyme was tightly bound to cores of HVJ and, therefore, its presence could not be explained by binding of host cell enzyme to the surface of virions. Properties of the virus-derived enzyme and particulate fractions of host cell homogenates were similar. Antiserum against nucleocapsids of HVJ inhibited guanylate cyclase activity of HVJ and particulate fractions of cells such as chorioallantoic membrane and rat liver, while soluble guanylate cyclase was not inhibited by antiserum. The biological significance and origin of guanylate cyclase found in HVJ are obscure and await further study.