[α-³²P] NTP Binding to Diphtheria Toxin and Light Signal Transmission to the Toxin through a Microsomal Fraction of Neurospora crassa

Abstract

Diphtheria toxin with the molecular mass of 60 kDa was detected to be capable of binding [α-³²P] ATP, [α-³²P] GTP and [α-³²P] UTP. The binding of [α-³²P] ATP was prevented in the presence of 10^-3 M ATP or GTP and that of [α-³²P]GTP was completely prevented in the presence of 10^-4 M ATP, GTP or UTP. CTP at a concentration of 10^-4 M stimulated the binding of the above three labeled nucleotides. Diphtheria toxin was auto-[³²P]ADP-ribosylated. This was prevented in the presence of 10^-3 M ATP, GTP or UTP. At 10^-5 M NAD was stimulated the binding of [α-³²P] ATP and [α-³²P] GTP but at 10^-5 M it inhibited it. UV-A light irradiation stimulated the binding of [α-³²P]ATP and [α-³²P] GTP to 58 kDa and 77 kDa, and [α-³²P]GTP to 83 kDa and 129 kDa proteins in the microsomal fraction of band strain of Neurospora crassa. NAD at 10^-5 M stimulated the binding of [α-³²P] ATP to 58 kDa and 77 kDa proteins. In the case of [α-³²P] GTP, 10^-5 M NAD reduced the back ground binding of [α-³²P] GTP, and further the presence of diphtheria toxin reduced the background binding of [α-³²P] GTP to these four proteins. UV-A light stimulated the binding of [α-³²P] ATP and [α-³²P] GTP to diphtheria toxin in the presence of the microsomal fraction.