Temperature-determined enzymatic functions in octopine dehydrogenase.

Area of Science:

• Biochemistry
• Enzymology
• Marine Biology

Background:

• Octopine dehydrogenase is a monomeric enzyme found in the scallop Pecten maximus L.
• Enzymes in poikilotherms often display unique temperature-dependent behaviors.
• Understanding enzyme function across temperatures is crucial for comprehending biological regulation.

Purpose of the Study:

• To investigate the temperature dependence of key enzymatic functions of octopine dehydrogenase.
• To explore the thermodynamic basis for observed temperature independence.
• To analyze the activation energy parameters in relation to enzyme turnover.

Main Methods:

• Enzyme extraction from Pecten maximus L.
• Measurement of dissociation constants for coenzyme complexes.
• Determination of Michaelis constants (Km) for NAD, NADH, and D-octopine.
• Analysis of temperature dependence of Vmax to calculate activation energy parameters (ΔH≠).

Main Results:

• Six enzymatic functions, including dissociation constants and Km values for NAD, NADH, and D-octopine, were found to be temperature-independent.
• A low activation enthalpy (ΔH≠) was observed for octopine dehydrogenase.
• The enzyme exhibits a limited change in turnover number across a physiological temperature range (5–35 °C).

Conclusions:

• Octopine dehydrogenase possesses a temperature-regulatory mechanism ensuring stable NAD, NADH, and D-octopine complex levels.
• The observed temperature independence is likely driven by specific entropic contributions to binding.
• The low activation enthalpy contributes to the enzyme's functional stability across varying temperatures, a common trait in poikilothermic enzymes.