Cations in component reactions of 'malic' enzyme catalysis

Area of Science:

• Biochemistry
• Enzymology
• Plant Science

Background:

• Malic enzyme (EC 1.1.1.40) plays a role in metabolic pathways.
• Understanding enzyme kinetics and substrate specificity is crucial for biochemical research.

Purpose of the Study:

• To purify malic enzyme from wheat germ.
• To investigate the enzyme's catalytic activities, specifically decarboxylation and hydrogenation of oxaloacetic acid and its esters.
• To elucidate the role of carboxyl groups and cations in enzyme-substrate interactions.

Main Methods:

• Enzyme purification (300-fold) from wheat germ.
• Enzymatic assays to study decarboxylation and hydrogenation reactions.
• Analysis of substrate structure-activity relationships.

Main Results:

• The free 1-carboxyl group is essential for oxaloacetate interaction with the enzyme via cations.
• The free 4-carboxyl group is necessary for decarboxylation but not essential for hydrogenation.
• Cations inhibit the hydrogenation of oxaloacetic acid at high concentrations, but not that of 4-ethyl oxaloacetate.

Conclusions:

• Wheat germ malic enzyme exhibits distinct requirements for its carboxyl groups during catalysis.
• Cation concentration influences the enzyme's activity, suggesting a role in regulating metabolic flux.
• A potential inhibitory mechanism involving cations was proposed, offering insights into enzyme regulation.