Activation of Sendai Virus Infectivity by an Enzyme in Chicken Amniotic Fluid

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Abstract
Sendai virus grown in LLC-MK2 cells is known to have low infectivity, no detectable haemolysing ability and predominantly uncleaved F glycoprotein. Treatment of such virus with chicken amniotic fluid resulted in a 103- to 104-fold increase in infectivity, the development of haemolysing ability, and cleavage of the F glycoprotein. The ‘Sendai activating enzyme’ (SAE) responsible for these effects required the presence of 1 mm-Ca2+ ions for maximum activity. It was inhibited by phenylmethylsulphonyl fluoride and soybean trypsin inhibitor but was unaffected by sulphydryl-blocking agents. The results of gel filtration tests suggested that the molecular weight of SAE was about 55000. SAE may be the natural proteolytic activator of Sendai virus in a soluble form.