4.1 Enzyme–Substrate Interaction

Module I – Molecular Foundations of Plant Biochemistry

1. Introduction to Enzymes

Enzymes are biological catalysts that accelerate biochemical reactions without being consumed. In plant systems, nearly every metabolic reaction—from photosynthesis to pigment synthesis—is enzyme-mediated.

Without enzymes, plant metabolism would proceed too slowly to sustain life, growth, and productivity.

Enzymes are primarily proteins with highly specific three-dimensional structures that determine their function.

2. Enzyme–Substrate Binding

The substrate is the molecule upon which an enzyme acts. The region of the enzyme that binds the substrate is called the active site.

Models of Interaction

Model Description Biochemical Meaning
Lock and Key Model Rigid active site matches substrate shape Explains high specificity
Induced Fit Model Active site changes shape upon binding Explains flexibility and regulation

3. Factors Affecting Enzyme Activity

Optimal enzyme conditions vary among plant tissues and developmental stages.

4. Enzyme Kinetics (Conceptual Overview)

Enzyme kinetics describes how reaction rate changes with substrate concentration.

In horticultural crops, enzyme kinetics determine sugar accumulation, pigment synthesis, ripening speed, and stress adaptation.

5. Enzyme Inhibition

Type Mechanism Horticultural Example
Competitive Inhibitor competes with substrate Metabolic regulation
Non-competitive Inhibitor binds elsewhere Stress-induced metabolic changes

Understanding inhibition helps interpret herbicide action, stress damage, and metabolic disorders.

6. Applied Interpretation in Horticulture

Enzyme–substrate interactions form the biochemical engine that determines crop productivity, quality, and stress response.

7. Reflection Questions