Photochemical Release of ATP from "Caged ATP" Studied by Time-Resolved Infrared Spectroscopy

Rapid scan Fourier transform infrared (FTIR) spectroscopy and time-resolved single wavelength infrared (IR) spectroscopy have been used to follow the photochemical release of adenosine 5'-triphosphate (ATP) from P3-( 1 -(2-nitrophenyl)ethyl) adenosine 5'-triphosphate (caged ATP). Vibrational difference spectra for the formation first of the aci-nitro anion intermediate and subsequently of ATP and the byproduct(s) were obtained by rapid scan FTIR spectroscopy in the millisecond-to-second time domain. Vibrational modes of the phosphate groups of ATP and caged ATP in the range 1250-900 cm-I could be assigned on the basis of triple and single l8O labeling in caged ATP at the terminal phosphate group and at the bridging oxygen between the terminal phosphate and the 1-(2-nitrophenyl)ethyl group, respectively. The rapid formation and subsequent decay of the aci-nitro anion intermediate were monitored by single-wavelength time-resolved IR spectroscopy at 125 1 cm- ' (predominantly a PO2- mode of caged ATP and the aci-nitro intermediate). The appearance of the free y-phosphate group of ATP was monitored at 1119 cm-I (P03'- mode of ATP). Decay of the aci-nitro anion intermediate and formation of ATP were well fitted by single exponentials to give a mean rate constant of 218 & 33 s-' at pH 7 and 22 OC.