Probing the Iron-sulphur Proteins : a Biochemist's View of Spectroscopic Methods

— Biochemists routinely use UV/visible spectrophotometry as a means of identifying and measuring the quantity of many biological compounds. When a new type of compound is isolated however, the method is often unhelpful in determining its chemical nature, and other spectroscopic methods must be used. The iron-sulphur proteins have recently been recognised as major components of bioenergetic systems such as respiration and photosynthesis. They represent a totally new type of biological compound. The simplest types of iron-sulphur proteins, the ferredoxins, have been investigated by a wide range of spectroscopic methods, including magnetic resonance and Mossbauer spectroscopy. Such methods involve problems in the preparation of concentrated, pure samples, and the work requires a close cooperation between the preparative biochemist and the spectroscopist. The results of application of different spectroscopic techniques on the eightiron ferredoxin from Clostridium pasteurianum are described, and the results are compared with those from a chemical analog of the iron-sulphur cluster. The protein clearly has an influence on the properties of the iron-sulphur cluster, as shown by modifications to its oxidation-reduction potential and reactivity. The applications of Mossbauer spectroscopy are being extended to the more complex iron-sulphur proteins such as nitrogenase, and to the photochemical reactions of photosynthesis.