Fig. 3. In vivo [³²P]ATP binding assays were used to show saturable, external binding in the range of 1-30 nmoll^-1 [³²P]ATP (A). Each point represents the mean ± S.D. of at least three trials. A Scatchard plot of this data infers a single class of external [³²P]ATP binding sites with an apparent K_d of approximately 23 nmoll^-1 and a B_max of 110 pmoll^-1 (B). The estimate of the number of surface [³²P]ATP binding sites is approximately 7.023x10⁵ receptors cell^-1.