ciclase

Ciclase, also spelled cyclase in English, designates an enzyme that catalyzes the formation of a cyclic compound from a linear substrate. The term is used across biology to describe several enzyme families that generate cyclic nucleotides or other cyclic molecules. The best-known examples are adenylyl cyclases, which convert ATP to cyclic AMP; guanylyl cyclases, which convert GTP to cyclic GMP; and ADP-ribosyl cyclases, which produce cyclic ADP-ribose from NAD+. In bacteria, diguanylate cyclases generate cyclic di-GMP, a second messenger that regulates biofilm formation and motility, while diadenylate cyclases synthesize cyclic di-AMP from two ATP molecules.

Mechanism and structure vary among cyclases, but many share the need for divalent metal ions such as magnesium or manganese and a catalytic domain that binds nucleotide substrates. Some cyclases are membrane-bound and regulated by receptor signaling or ionic conditions, whereas others are soluble cytosolic enzymes. The diversity of catalytic domains gives rise to different cyclization reactions and product specificities, from single-nucleotide cyclic messengers to more complex cyclic dinucleotides.

Biological roles are broad and context-dependent. In animals and plants, cyclic AMP and cyclic GMP act as second messengers that regulate metabolism, gene expression, vision, and vascular tone. In bacteria, cyclic di-nucleotides control biofilm formation, cell cycle progression, and stress responses. Because of their central role in signaling networks, cyclases are frequent subjects of study in biochemistry and pharmacology. Therapeutic strategies more commonly target downstream effectors or the breakdown of cyclic nucleotides by phosphodiesterases than the cyclases themselves, though some contexts explore direct cyclase modulation.

Etymology and usage: the name derives from the Greek root for circle or ring, reflecting the cyclic nature of the products. Variants exist in different languages, with terms such as ciclasa used in some linguistic contexts.