Iron-sulfur clusters biological activity

Biological Iron-Sulfur Clusters with Catalytic Activity... 

The discovery of the different dinuclear or cuboidal-type biological iron-sulfur clusters is associated with their natural occurrence in two oxidation states. They can all function as one-electron transferring agents. This redox function has been well established in many studies over a period of almost five decades [1-5], However, electron transfer is generally not considered to be a catalytic activity. It is typically a stoichiometric transfer between two complex redox proteins. Mechanistically, it is probably best described as outer sphere or not involving the breaking and making of covalent bonds other than those related to hydrons. 

Aconitase was the first protein to be identified as containing a catalytic iron-sulfur cluster [24-26]. It was also readily established that the redox properties of the [4Fe-4S](2+ 1+) cluster do not play a role of significance in biological functioning the 1 + oxidation state has some 30% of the activity of the 2+ state [25], Since then several other enzymes have been identified or proposed to be nonredox iron-sulfur catalysts. They are listed in Table 2. It appears that all are involved in stereospecific hydration reactions. However, these proteins are considerably less well characterized than aconitase. In particular, no crystal structural information is available yet. Therefore, later we summarize structural and mechanistic information on aconitase, noting that many of the basic principles are expected to be relevant to the other enzymes of Table 2. 

This volume begins with a discussion of iron sulfur clusters, a familiar topic to bioinorganic chemists and one that has not lost its appeal. Although long known for their role in biological electron transfer, they have recently been shown also to possess catalytic activity through subsite specific chemistry, wherein one of the iron atoms in the cube catalyzes chemical transformation at its particular corner. To reproduce such disymmetry in an... 

Synchrotron-based nuclear resonance methods have revealed the vibrational dynamics of the iron atom in numerous systems, including alloys, amorphous materials, nanomaterials, and materials under high pressure. The above-mentioned selectivity for the probe nucleus is particularly valuable for biological macromolecules, which may contain many thousands of atoms, but a localized active site is often the true center of interest. Since its availability, NRVS has been applied to study the vibrational dynamics of Fe in proteins, porphyrin model compounds, " and iron-sulfur clusters. It is shown that NRVS can provide frequencies, amplitudes, and directions for Fe vibrations in the samples. It helps to clarify mode assignments in vibrational spectra and reveals many important vibrational modes of Fe that cannot be seen by other methods. In particular, NRVS reveals low-frequency motions of the Fe down to below 100 cm that control biological reactions. The applications presented here use Fe as the probe nucleus, but the principle applies to other Mossbauer isotopes such as " Sn, Kr, Ni, and Zn if appropriate sources are available. 

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