GLOSSARY

Enzyme Degradation breaks down enzyme protein during renewal.

Enzyme abundance reflects protein synthesis and degradation; gene expression, RNA, protein quantity and measured activity are different layers. Induction and repression need definition because expression and activity can differ. Constitutive does not mean a perfectly constant amount under all conditions. In exercise interpretation, long-term capacity changes must be separated from rapid activation of existing enzyme and from actual pathway flux rather than treating them as interchangeable findings.

Adding or removing a chemical group can alter enzyme activity, location, stability or interactions. Phosphorylation is not universally activating; direction depends on protein and site. Acetylation, methylation and small-protein attachment have varied roles and are not all degradation labels. Post-translational changes must be distinguished from new protein production because their speed and persistence can differ, even when they influence the same pathway or exercise response.

Flux control is usually distributed across steps, substrate supply and demand. Rate-limiting is condition-dependent rather than identifying an enzyme that always commands the whole pathway. A committed step marks more specific entry into a pathway and need not carry the greatest control. Increasing one enzyme or supplying its precursor does not guarantee greater network flux or performance without considering the wider system.

Location determines access to substrates, cofactors and local conditions. Cytosol, mitochondrial matrix, peroxisomes and nucleus are not equivalent environments. Microsomal usually refers to a laboratory membrane fraction largely derived from endoplasmic reticulum, not a normal independent organelle in living cells. Direct transfer of intermediates between enzymes requires evidence; proximity or membership of the same compartment alone does not establish substrate channeling or its magnitude.

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.

Training can change enzyme abundance, regulation or activity capacity depending on mode, intensity, volume and training history. An acute session response is not the same as chronic adaptation. Oxidative or glycolytic markers describe only part of performance; oxygen delivery, fuel stores and neural coordination also matter. Practical assessment therefore combines performance and recovery outcomes with adequate nutrition and the actual training program rather than relying on one enzyme marker.