The chemistry of nitrosyl porhyrins, pharmacology of dopamine receptors, and biochemistry of adenylyl cyclase

Abhay Devadas Kini, Purdue University

Abstract

Nitrosyl cobalt tetraphenylporphyrins CoT(p-X)PP(NO) (X = H, OMe, No2) substituted at the meso para-phenyl position were prepared and the metal-NO interaction was probed using cyclic voltammetry and reflectance infrared spectroelectrochemistry. Cyclic voltammetry indicated that porphyrin ring substitution strongly affects the porphyrin ring based, first oxidation potential. Substitution at the porphyrin ring had significantly less influence on the second, metal-based oxidation potential. It was demonstrated that the strength of the cobalt nitrosyl interaction, as monitored by ν(N≡O), can be controlled by varying the substituents on the porphyrin ring. Reflectance infrared spectroelectrochemical (SEC) experiments were undertaken to further investigate the electrochemical properties. SEC experiments allowed, for the first time, the observation of ν(N≡O) bands for the first and second oxidation products of the nitrosylated metalloporphyrins. The ν(N≡O) stretches indicated that electron donating functional groups weakened Co-NO interaction whereas electron withdrawing groups strengthened it. The effect of protein tyrosine kinase (PTK) inhibitors, genistein and tyrphostin 51 on adenylyl cyclase (AC) activity was investigated in insect cells. It was discovered that both PTK inhibitors were able to inhibit cyclic adenosine monophosphate (cAMP) production. Three AC isoforms (ACI, ACIV and AC VI) were expressed in insect cells in order to identify whether tyrosine phosphorylation is a mode of regulation common to all AC isoforms. PTK inhibitors were able to inhibit cAMP levels in cells expressing AC IV and AC VI. However, cAMP levels in cells expressing ACI could not be inhibited by PTK inhibitors. In all cases, both genistein and tyrphostin 51 were able to inhibit PTK activity. Insect cells grown in serum free media were unable to respond to inhibition of cAMP levels by PTK inhibitors. Hence there is very strong possibility that the PTK involved in this mode of regulation is activated by serum.

Degree

Ph.D.

Advisors

Morimoto, Purdue University.

Subject Area

Biochemistry|Chemistry

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