Opines are low molecular weight compounds found in plant crown gall tumors or hairy root tumors produced by parasitic bacteria of the genus Agrobacterium. Opine biosynthesis is catalyzed by specific enzymes encoded by genes contained in a small segment of DNA (known as the T-DNA, for 'transfer DNA'), which is part of the Ti plasmid, inserted by the bacterium into the plant genome. The opines are used by the bacterium as an important source of nitrogen and energy. Each strain of Agrobacterium induces and catabolizes a specific set of opines. There are at least 30 different opines described so far.
Chemically, opines fall into two major structural classes:
1. The vast majority are secondary amine derivatives formed by condensation of an amino acid, either with a keto acid or a sugar. The first subcategory includes the nopaline and octopine families. The nopaline family (nopaline, nopalinic acid, leucinopine, glutaminopine, succinamopine) is formed when alpha-ketoglutarate serves as the keto substrate in the condensation reaction. The octopine family (octopine, octopinic acid, lysopine, histopine) is formed when pyruvate is involved in the condensation reaction.
The second subcategory includes the mannityl family (mannopine, mannopinic acid, agropine, agropinic acid) formed by the condensation of an amino-acid with mannose.
The name opine comes from octopine, the first opine discovered in 1927, not in crown galls, but in octopus muscle. According to Oxford English Dictionary, the word opine was first used in print in 1977. Usually, the name of newly discovered opines has the ending "-opine". Exceptions are nopaline and strombine. On the other hand, not all molecule names ending in "-opine" are opines. For example, atropine, stylopine, europine, and lycopine belong to different classes of molecules.