PROBING THE IRON-SULPHUR PROTEINS : A BIOCHEMIST'S VIEW OF SPECTROSCOPIC METHODS

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Abstract
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 spec­ troscopic 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 ferredo- xins, have been investigated by a wide range of spectroscopic methods, including magnetic reso­ nance and Mossbauer spectroscopy. Such methods involve problems in the preparation of concen­ trated, 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 eight- iron 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 poten­ tial 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 photo­ synthesis.

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