Inhibitors of abscisic acid 8'-hydroxylase

Biochemistry. 2000 Nov 7;39(44):13614-24. doi: 10.1021/bi0014453.

Abstract

Structural analogues of the phytohormone (+)-abscisic acid (ABA) have been synthesized and tested as inhibitors of the catabolic enzyme (+)-ABA 8'-hydroxylase. Assays employed microsomes from suspension-cultured corn cells. Four of the analogues [(+)-8'-acetylene-ABA, (+)-9'-propargyl-ABA, (-)-9'-propargyl-ABA, and (+)-9'-allyl-ABA] proved to be suicide substrates of ABA 8'-hydroxylase. For each suicide substrate, inactivation required NADPH, increased with time, and was blocked by addition of the natural substrate, (+)-ABA. The most effective suicide substrate was (+)-9'-propargyl-ABA (K(I) = 0.27 microM). Several analogues were competitive inhibitors of ABA 8'-hydroxylase, of which the most effective was (+)-8'-propargyl-ABA (K(i) = 1.1 microM). Enzymes in the microsomal extracts also hydroxylated (-)-ABA at the 7'-position at a low rate. This activity was not inhibited by the suicide substrates, showing that the 7'-hydroxylation of (-)-ABA was catalyzed by a different enzyme from that which catalyzed 8'-hydroxylation of (+)-ABA. Based on the results described, a simple model for the positioning of substrates in the active site of ABA 8'-hydroxylase is proposed. In a representative physiological assay, inhibition of Arabidopsis thaliana seed germination, (+)-9'-propargyl-ABA and (+)-8'-acetylene-ABA exhibited substantially stronger hormonal activity than (+)-ABA itself.

Publication types

  • Comparative Study

MeSH terms

  • Abscisic Acid / agonists
  • Abscisic Acid / analogs & derivatives
  • Abscisic Acid / chemistry
  • Abscisic Acid / metabolism
  • Binding, Competitive
  • Cytochrome P-450 Enzyme Inhibitors*
  • Cytochrome P-450 Enzyme System / chemistry
  • Cytochrome P-450 Enzyme System / metabolism
  • Enzyme Inhibitors / chemical synthesis
  • Enzyme Inhibitors / chemistry*
  • Enzyme Inhibitors / metabolism
  • Germination
  • Hydroxylation
  • Kinetics
  • Mixed Function Oxygenases / antagonists & inhibitors*
  • Mixed Function Oxygenases / chemistry
  • Mixed Function Oxygenases / metabolism
  • Plant Growth Regulators / chemical synthesis
  • Plant Growth Regulators / chemistry
  • Plant Growth Regulators / metabolism
  • Plant Proteins
  • Seeds / enzymology
  • Seeds / physiology
  • Substrate Specificity

Substances

  • Cytochrome P-450 Enzyme Inhibitors
  • Enzyme Inhibitors
  • Plant Growth Regulators
  • Plant Proteins
  • Abscisic Acid
  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • abscisic acid 8'-hydroxylase