Fig. 5. Lineweaver-Burk plots for the inhibition of the adenylyl cyclase domain of EF (EF3, amino acid residues 291-800) by four acyclic nucleotide phosphonates: PMEApp, PMPApp, PMEDAPpp, and PMPDAPpp. The adenylyl cyclase assay was done in the presence of 17 pM EF3, 1 m M CaM, and 1 m M free Ca2+. The Km values (m M) for ATP determined in the presence of PMEApp, PMPApp, PMEDAPpp, and PMPDAPpp were 194 ± 21, 168 ± 10, 187 ± 19, and 186 ± 12, respectively. The Vmax values (ms-1) determined in the presence of PMEApp, PMPApp, PMEDAPpp, and PMPDAPpp were 4.7 ± 0.6, 4.4 ± 0.4, 4.6 ± 0.6, and 2.4 ± 0.05, respectively.