A chemical approach to systematically designate the pyranopterin centers of molybdenum and tungsten enzymes and synthetic models

The recent growth in the chemistry of the oxo-molybdenum enzymes has demons trated the need for developing systematic methods for naming and abbreviati ng the novel pterin cofactors that bind to the metal ion via the sulfur ato ms of an ene-1,2-dithiolate moiety. Historically, the term "molybdopterin" was coined to designate a special pterin that binds molybdenum and the moly bdenum-bound form was termed the "molybdenum cofactor". However, recent stu dies have demonstrated that this novel pterin also binds tungsten. Furtherm ore, considerable variation has been found in the pterin entity itself. Tak en together, these facts show that molybdenum- and tungsten-containing enzy mes possess a family of cofactors rather than a single "molybdenum cofactor ". This article proposes a unified methodology for describing these cofacto rs and their metal-free pterin units in light of recent results from protei n crystallography. The various numbering schemes that have been used for th is heterocycle are considered, as well as the IUPAC rules which are current ly being used for related tricyclic compounds. A unified methodology for un iquely designating and abbreviating each cofactor is proposed. The availabl e chemical and spectroscopic information on the pyranopterin entities that are present in the molybdenum and tungsten enzymes, the precursors to these centers, and synthetic pyranopterins are in part the basis of the systemat ic names and simplifying abbreviations. (C) 1998 Elsevier Science Inc. All rights reserved.