Enzyme

Definition

A biological macromolecule—almost always a protein, occasionally an RNA ribozyme—that functions as a catalyst, accelerating specific biochemical reactions without being consumed. Enzymes bind substrates at active sites, lower activation energy, and convert substrates to products with high specificity. In arthropods, enzymes mediate critical processes including digestion (proteases, lipases, carbohydrases in the midgut), cuticle sclerotization (phenoloxidases, laccases), venom toxicity (phospholipases, hyaluronidases in spiders and hymenopterans), pheromone biosynthesis (desaturases, reductases), and detoxification of plant allelochemicals or synthetic insecticides (cytochrome P450 monooxygenases, glutathione S-transferases, esterases). Enzyme activity is regulated by pH, temperature, cofactors, inhibitors, and post-translational modification; many arthropod enzymes exhibit cold-adaptation or heat-stability extremes matching their ecological niches.

Etymology

From German Enzym, coined 1878 by Wilhelm Kühne from Greek en- 'in' + zymē 'leaven, yeast', reflecting early recognition of fermentation catalysts.

Example

Lepidopteran larvae feeding on cyanogenic plants upregulate β-cyanoalanine synthase, a detoxifying enzyme that converts cyanide to the less toxic amino acid β-cyanoalanine, allowing specialization on otherwise lethal host plants.

Synonyms

• biocatalyst

Related Terms

• substrate
• active site
• cofactor
• inhibitor
• metabolic pathway
• digestive enzyme
• detoxification enzyme
• phenoloxidase
• cytochrome P450
• esterase
• Protease
• lipase
• carbohydrase
• ribozyme
• pseudoenzyme

Usage Notes

Enzyme names conventionally end in -ase with a prefix indicating substrate or reaction type (e.g., lactase, polymerase). In arthropod physiology, distinguish constitutive enzymes (always present) from inducible enzymes (synthesized in response to substrate or stressor, such as insecticide exposure). Specificity varies: some enzymes act on single substrates (absolute specificity), others on structurally related groups (group specificity). Temperature optima often differ between temperate and tropical species; enzyme kinetics parameters (Km, Vmax) are used to compare metabolic capacity across populations or species. Pseudoenzymes—catalytically inactive homologs—retain regulatory or scaffolding roles in some signaling pathways.