CHEMICAL PACEMAKERS : III. ACTIVATION ENERGIES OF SOME RATE-LIMITING COMPONENTS OF RESPIRATORY SYSTEMS

Area of Science:

• Biochemistry
• Enzymology
• Cellular Respiration

Background:

• Previous studies determined activation energies for succinate oxidation using beef heart extract.
• Succinate-fumarate oxidation involves succino-dehydrogenase and cytochrome-cytochrome oxidase components.

Purpose of the Study:

• To further investigate the activation energies of components within the succinate-fumarate enzyme system.
• To determine if activation energies are associated with enzymes or specific reaction steps.

Main Methods:

• Enzyme kinetics studies using beef heart extract.
• Measuring activation energies via Arrhenius equation plots.
• Utilizing p-phenylenediamine oxidation and pyrophosphate/cyanide inhibition models.

Main Results:

• Oxidation of p-phenylenediamine yielded an activation energy of 9,500 calories.
• Pyrophosphate inhibition resulted in an activation energy of 17,500 calories.
• Cresyl blue substitution for oxidase yielded activation energies of 18,500 and 22,000 calories.

Conclusions:

• Activation energies are not inherent to enzymes but are tied to specific catalytic reaction steps.
• These findings elucidate the energetic properties of individual steps in the respiratory chain.