Incubation of human thrombocytes in the presence of [3H]palmitic acid leads to incorporation of this fatty acid into the alpha subunit of Gs as described [Linder et al., Proc. Natl. Acad. Sci. USA 90 (1993) 3675-3679; Degtyarev et al., Biochemistry 32 (1993) 8057-8061] but also into the catalyst of adenylyl cyclase which has not been recognized before. Treatment of labeled membranes with hydroxylamine released the label from both components. Label incorporated into the catalyst could be identified as [3H]palmitate. At the same time chemical deacylation caused partial loss of adenylyl cyclase activity.