GLOSSARY

Catalytic Mechanism is the molecular means by which an enzyme facilitates reaction.

Enzymes lower barriers through suitable substrate orientation, active-site chemistry and transition-state stabilization. A transition state is not a stable intermediate that accumulates. Catalysis may involve proton transfer, temporary covalent bonds or metal-ion assistance; enzymes do not all use one mechanism. Mechanistic description supports biochemical understanding but alone cannot demonstrate a supplement benefit or an improvement in sports performance without relevant outcome evidence.

An enzyme accelerates a reaction by lowering its activation barrier, without changing the final equilibrium or reaction free-energy difference. It is not consumed overall during a catalytic cycle, although it can be degraded or inactivated. Most enzymes are proteins, but catalytic RNA also exists. More enzyme increases reaction rate only when other constraints allow it; substrate supply, products and conditions still matter.

Gibbs free energy describes thermodynamic favorability under specified conditions, not reaction speed by itself. Exergonic and endergonic concern free-energy change; exothermic and endothermic concern heat, so the pairs are not interchangeable. Concentrations and conditions alter actual values. Standard-condition numbers cannot simply be transferred unchanged to every cell or interpreted as the entire energy content of a meal. Thermodynamic direction and physiological rate answer different questions.

For example, after training changes an enzyme result, first ask whether it was measured in blood, tissue or purified protein. Then assess assay conditions, nutrition and time since the last session alongside actual performance; this comparison helps distinguish a regulatory response from a nutritional deficiency or a presumed supplement need.

Specificity may concern substrate identity, reaction type or molecular stereochemistry; these are related but distinct properties. Some enzymes accept several related substrates while others have a narrower range. A family name alone cannot establish every member's exact function. Nutritionally, a similar molecule or possible binding does not prove effective processing through the intended pathway; correct substrate, reaction and conditions must be considered together.

Binding, conformational adjustment, chemistry and product release are connected steps of an enzyme cycle, and each step's rate can matter. Lock-and-key is a useful simplified teaching model but incompletely represents protein flexibility; induced fit and selection among existing conformations give a more dynamic view. Tighter binding does not always produce faster turnover or more product, because chemical conversion and release must also occur.

Measured activity is conversion per time under assay conditions rather than simply protein abundance. A substrate-rich assay may reveal potential capacity, while living tissue has different constraints and regulation. Units, tissue normalization and preparation methods are needed for comparison. Blood activity is not identical to intramuscular activity; laboratory changes require exercise timing, symptoms and tissue origin rather than being read as direct performance measures or a standalone diagnosis.