Linked functions heme proteins

The human body contains lactoperoxidase, a product of exocrine secretion into milk, saliva, tears, etc., and peroxidases with specialized functions in saliva, the thyroid, eosinophils,219 and neutrophils.220 The functions are largely protective but the enzymes also participate in biosynthesis. Mammalian peroxidases have heme covalently linked to the proteins, as indicated in Fig. 16-12 220 222a... 

It has long been established that the functional unit of cytochrome oxidase contains four redox-active metal centres. Two of these, cytochromes a and a3, contain heme A (Fig. 5-23) coordinated in different ways in subunit I. The heme group is not covalently linked to the protein. The main structural features are the carbonyl group at position 8 and the isoprenoid chain at position 2 of the porphyrin ring. 

Metalloproteins constitute a distinct subclass of proteins that are characterized by the presence of single or multiple metal ions bound to the protein by interactions with nitrogen, sulfur, or oxygen atoms of available amino acid residues or are complexed by prosthetic groups, such as heme, that are covalently linked to the protein. These metals function either as catalysts for chemical reactions or as stabilizers of the protein tertiary structure. Protein-bound metals may also be labile and, as such, be subject to transport, transient storage, and donation to other molecular sites of requirement within tissues and cells. 

X. Equilibrium Involving Oxygen and Carbon Monoxide and Heme Pkoteins 471 CO as a respiratory poison. CO and O2 combination as identically linked functions. Haldane s laws. Demonstration of interdependence of these. Heat of the exchange reaction involving O2 and CO. CO-O2 partition coefficients of various heme proteins and their relation to span. Dependence of CO equilibrium on light. 

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