Many times C-2 and C-8 substituted adenosine photoaffinity nucleotide analogs differ markedly in their ability to serve as substrates for ATP specific nucleotide binding proteins. Substitution of an azido group for a hydrogen at the C-8 position of the adenine unit has been shown to alter the conformation of the purine ring with respect to the ribose sugar (Sarma et al., 1974; Tavale and Sobell, 1970). This change in conformation from anti to syn that is adopted by the purine ring about the N-glycosidic bond following substitution at the C-8 position will often drastically alter the suitability of the analog as a substrate. The 2-azido derivatives have been reported to exist predominantly in the anti conformation, whereas the 8-azido analog is mainly in the syn form (Czarnecki, 1984). Native ATP exist predominantly in the anti conformation and Mn2+ coordination has been shown to stabilize ATP in the anti conformation (King et al., 1989). This difference in conformation between 8N3ATP and 2N3ATP analogs has been utilized to successfully map the purine ring binding domain peptides to opposite sides of the V1 pocket of the b chain of the microtubule associated protein dynein (King et al., 1989)
REFERENCES Czarneki, J.J. (1984) Biochim. Biophys. Acta 800: 41-51. King, S.M., Haley, B.E. and Witman, G.B. (1989) J. Biol. Chem. 264: 10210-10218. Sarma, R.H., Lee, C.H., Evans, F.E., Yathindra, N. and Sundralingam, M. (1974). J. Am. Chem. Soc. 96: 7337-7348. Tavale, S.S. and Sobell, H.M. (1970) J. Mol. Biol. 48:109-123.
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