Proteins donor

The structures of type II copper sites have not as yet generated as much interest, but the hetero-dinuclear structures of type IIC copper sites and the unusual protein donor ligands found in type IIB copper sites are noteworthy. The synthetic model approach to gain insight into the structures and functions of these types of copper sites will be also described. The diverse functions of a variety of proteins containing type IIA copper sites inspired many chemists to mimic the functions with synthetic copper complexes, even though the spectroscopic properties of the complexes are not unusual. Results of these studies will be reviewed and different aspects of the reactions relating to enzymatic catalysis will be discussed. 

Hemerythrin is the best studied example and high-resolution X-ray data are available for the deoxy (176), oxy (176), met (177), and azido-met (177) forms. Extensive spectroscopic studies have also been carried out on these forms and on the semi-met Fe" Fe form 178). The active site structure of hemerythrin is illustrated in Fig. 40. The two iron atoms are bridged by an oxygen donor (OH or 0 ) and by two carbox-ylates, one aspartate and one gluamate. The remaining protein donors are five histidine residues, three coordinated to one iron and two to the other. In the deoxy form one iron atom is five coordinate and this vacant site can be occupied by dioxygen in oxyhemerythrin or by other... 

B. Zingales, C. Camiol, R. M. de Lederkremer, and W. Colli, Direct sialic acid transfer from a protein donor to glycolipids of trypomastigote forms of Trypanosoma cruzi, Mol. Biochem. Parasitol., 26 (1987) 135-144. 

Four structural classes of Fe-S centre have been identified to date these are depicted in Fig. 13. All of them feature high-spin tetrahedral Fe(II) or Fe(III) coordinated typically by four sulfur donors. Apart from the monomeric centre found in proteins known as rubredoxins, they are all clusters that contain both protein donors and inorganic bridging (p) sulfido ligands. Most of our knowledge stems from studies made on the small electron-transport proteins known as ferredoxins (Fd s) and from work on model compounds. Figure 14 shows the structure of a ferredoxin isolated from the anaerobe Peptococcus aerogenes [165]. 

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