Haem* enzymes

Figure 2.11 Metal coordination sites of crystallographically characterized mononuclear non-haem enzymes. Reprinted with permission from Que and Ho, 1996. Copyright (1996) American Chemical Society.

Cytochrome P450 enzymes are important in pharmaceutical research and development, because of their roles in drug metabolism.129 They are a ubiquitous class of haem enzymes, which act as monooxygenases in a wide variety of biological reactions. 

Haem enzymes Bacterial/plant/fungal peroxidases Cytochrome c peroxidase(yeast) haemB (His) tryptophan 3.1.1.1... 

Non-haem enzymes Ribonucleotide reductase dinuclear iron deoxyribonucleotide synthesis Tyrosine 3.2.1. 

Recently, we have suggested an alternative to the iron-catalysed HO -dependent mechanism to explain the cleavage and consequent loss of viscosity of synovial fluid HA during rheumatoid arthritis [16]. This mechanism involves the haem enzyme myeloperoxidase (MPO) and the production of the strong oxidant hypochlorous acid (HOC1) by the following reaction ... 

Reactions which generate unstable intermediates with a potential to chemiluminesce are well-known in living cells. Such examples include haem enzymes NADPH oxidase (Allen et al., 1972), cytochrome P-450 (Cadenas et al., 1980), cyclooxygenase (Marnett et al., 1974) and the non-haem iron-containing enzyme lipoxygenases (Veldink et al., 1977 Boveris et al., 1980). 

The so-called Soret band, a strong absorption at ca 410 nm, is typical of haeme enzymes. 

In liver, muscle and other tissues iron is taken up by the cells when transferrin saturation levels are high and deposited first in ferritin and subsequently transferred to haemosiderin. This pool of ferritin iron is most likely used within these cells to meet requirements for synthesis of haem enzymes, myoglobin and other non-haem iron proteins. The ferritin can also store iron released from the breakdown of such iron containing proteins in the course of their turnover. Mobilisation of iron from these tissues once again probably involves reduction of iron to Fe2+ and its transfer across the cell membrane to transferrin. In such tissues the level of transferrin saturation seems likely to play a major role in determining the balance between deposition of iron in ferritin and its mobilization from the storage form. 

DNA/protein ratio. Furthermore, less abundant biomolecules such as carotenoids or haem enzymes or non-fluorescent drugs (e.g. cobalt octacarboxyph-thalocyanine) can be detected by taking advantage of the RR effect. These studies are particularly promising for elucidating metabolic processes in cells. 

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