EC numbers are used to describe enzyme reactions and are based on the recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (IUBMB). Unfortunately, not all known enzyme reactions have an EC number assigned yet. Until recently, these reactions were assigned so-called partial EC numbers where part of the numbers were replaced by dashes (e.g. EC 3.4.24.-). Partial EC numbers were used whenever the catalytic activity of the protein was not known exactly, or when the protein catalyzes a reaction which is known but not yet included in the IUBMB EC list. To distinguish between these two meanings, we have started to use the letter ‘n’ with a serial number instead of a dash ‘-’for enzymes with known catalytic activities. The serial numbers are included to ensure that each preliminary EC number is unique.
