GLOSSARY

Zymogen is an enzyme precursor with reduced activity or a maturation requirement.

Some enzymes are produced as relatively inactive precursors to control where and when they act. Proteolytic cleavage can activate them and is generally not a rapidly reversible switch in the same molecule like phosphate addition and removal. Maturation may also require folding or cofactor incorporation. Digestive proteases illustrate this principle, but their biology does not establish a general need for oral enzyme supplements in healthy athletes.

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.

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.