Biochemistry Enzyme Properties and Nomenclature

Enzyme Storage and Stability

• Enzymes can be preserved for a longer period at -20°C due to the inactivation of enzymes.
• 8°C is the ideal temperature for substrate and coenzymes.
• Room temperature is suitable for storing LDH (LD4 and LDS).

Enzyme Inhibition and Activation

• Hemolysis increases enzyme concentration, whereas lactescence or milky specimens decrease enzyme concentration.
• Inhibitors can bind to the enzyme-substrate complex, increasing inhibition with increasing substrate concentration.

Enzyme Nomenclature

• The Enzyme Commission (EC) standardized enzyme nomenclature in 1961, with revisions in 1972 and 1978.
• Enzymes are classified based on their biochemical functions, substrate, and reaction catalyzed, with a unique EC number.
• The first digit of the EC number places the enzyme into one of six classifications.

Enzyme Classification

• Oxidoreductases catalyze redox reactions (e.g., CO, LDH, MDH, ICD, G-6-PD).
• Uncompetitive inhibitors bind to the enzyme-substrate complex, increasing inhibition with substrate concentration.

Isoenzymes

• Isoenzymes have the same catalytic reaction but slightly different molecular structures.
• Fractionating isoenzymes enhances the importance of total enzyme activity.

Temperature Effects

• Increasing temperature usually increases the rate of chemical reactions by increasing molecular movement.
• Enzymes are active at 25°C, 30°C, or 37°C, with 37°C being the optimum temperature for enzymatic activity.
• The rate of denaturation increases with temperature, and is significant at 40°C-50°C.
• Refrigerated/freezing temperatures can reversibly inactivate enzymes.
• Repeated freezing and thawing can denature proteins and should be avoided.
• The temperature coefficient (Q10) indicates a two-fold increase in enzyme activity for every 10°C increase in temperature.

pH Effects

• Extreme pH levels can denature an enzyme or cause structural changes, affecting its ionic state.
• Most physiologic reactions occur in the pH range of 7-8.

Enzyme Basics

• Enzymes are proteins produced by living cells that catalyze chemical reactions in organic matter.
• Enzymes are measured by their activity, not absolute values.
• Enzymes are large molecules confined within cells unless membrane permeability allows them to enter the blood.
• Abnormal enzyme levels in serum can indicate organ damage.

Factors Affecting Enzyme Reactions

• Enzyme concentration: higher enzyme concentration increases the reaction rate.
• Substrate concentration: the reaction rate increases with substrate concentration until saturation kinetics.
• Cofactors: nonprotein entities that must bind to particular enzymes before a reaction occurs (e.g., NADP).
• Coenzymes: organic compounds that increase the velocity of an enzymatic reaction when their concentration increases.