Desmolase

Desmolase is a historical term used in biochemistry to describe enzymes that catalyze desmolization—the cleavage of a bond within a molecule to yield two fragments. The name implies bond scission without hydrolysis and, in many cases, without an immediate net addition of water or transfer of electrons, though some desmolases function as oxidative enzymes in which oxygen is incorporated during the cleavage.

In modern enzyme nomenclature, desmolase is not a formal EC class. Many activities once labeled desmolase are now described as lyases (EC 4.x) or, when associated with cytochrome P450 systems, as oxidoreductases that effect oxidative desmolization. The term persists mainly in historical or specialized literature and in reference to specific reactions rather than as a formal category.

A well-known historical example is cholesterol desmolase, also called side-chain cleavage desmolase, which catalyzes the cleavage of the cholesterol side chain to form pregnenolone and isocaproaldehyde during steroid biosynthesis. This activity is performed by a mitochondrial cytochrome P450 enzyme (CYP11A1, also known as P450scc) that uses NADPH and O2.

Desmolase-like activities have been reported in various organisms and metabolic pathways, where the enzyme cleaves a substrate to produce two fragments, potentially generating a double bond or opening a ring as part of the transformation. Today, such reactions are typically described in terms of their specific enzymes and mechanisms within the broader classes of lyases or oxidoreductases.