| Abstract: | Di(adenosine-5')oligophosphate nucleotides of general structure ApnA (n = 3-6) inhibited the protein kinase activity of homogeneous phorboid receptor. These nucleotides did not affect the phorboid binding activity. Ap4A competed for an ATP binding site on the phorboid receptor. Km for ATP was increased from 0.5 to 2 microM in the presence of 0.2 mM of Ap4A. KI was calculated to be approximately 0.1 mM. Ap4A-elicited inhibition of phorboid receptor kinase activity was independent of receptor concentration as well as of phosphoacceptor substrate concentration. |
