Other nitrogen pigments 4 Vitamin

The chemical composition of honey (Table 2.3) is dominated by glucose and fructose. Honey also contains many other valuable components, like enzymes, organic acids, mineral elements, nonprotein nitrogenous compounds, vitamins, aroma substances, and pigments. 

Cobalt compounds have been in use for centuries, notably as pigments ( cobalt blue ) in glass and porcelain (a double silicate of cobalt and potassium) the metal itself has been produced on an industrial scale only during the twentieth century. Cobalt is relatively uncommon but widely distributed it occurs biologically in vitamin B12 (a complex of cobalt(III) in which the cobalt is bonded octahedrally to nitrogen atoms and the carbon atom of a CN group). In its ores, it is usually in combination with sulphur or arsenic, and other metals, notably copper and silver, are often present. Extraction is carried out by a process essentially similar to that used for iron, but is complicate because of the need to remove arsenic and other metals. 

In this chapter, the metabolism of aromatic amino acids, including histidine, is examined. The aromatic amino acids are dietary essentials, with the exception of tyrosine, which can be formed from phenylalanine. Each of the amino acids has a unique metabolism, including the formation of important compounds other than proteins as neurotransmitters, pigments, and a vitamin. A number of metabolic diseases are also associated with aromatic amino-acid metabolism. An overall view of nitrogen economy and protein metabolism is discussed at the end of the chapter. 

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