cyclase

Cyclase is a general term for enzymes that catalyze the formation of cyclic compounds from linear substrates through cyclization reactions. The name is used across biology and biochemistry to indicate the ring-formation step in various metabolic pathways.

Two well-known families in eukaryotes are nucleotide cyclases: adenylyl cyclases convert ATP to cyclic adenosine monophosphate (cAMP), and guanylyl cyclases convert GTP to cyclic guanosine monophosphate (cGMP). Some are membrane-bound receptors activated by hormones or peptides, others are soluble cytosolic enzymes regulated by nitric oxide, calcium, or other factors. cAMP and cGMP serve as important second messengers, regulating processes from metabolism to gene expression.

In bacteria, cyclases generate cyclic dinucleotides such as cyclic di-GMP and cyclic di-AMP, signaling molecules that control biofilm formation, motility, and cell wall synthesis. Diguanylate cyclases (GGDEF family) synthesize cyclic di-GMP from two GTP units.

Terpene cyclases are another major class; they convert linear isoprenoid diphosphate substrates into cyclic terpenes, producing compounds such as limonene and pinene and contributing to aroma formation. These enzymes are central to natural product biosynthesis and metabolic diversity.

Because cyclases catalyze ring formation, their study illuminates structural strategies to stabilize reactive intermediates and achieve specific stereochemistry. The term cyclase can refer to several distinct enzyme families that share the common feature of catalyzing cyclization rather than simply transforming functional groups.