ABSTRACT
Phosphorus is an essential biological element that can be found in nu merous structures. The principal biochemical forms are phosphoanhydrides and phosphate mono-and diesters of alcohols, although a few phosphoramidates such as phosphocreatine and phosphoarginine are known (Fig. 1). In addition, sulfur-containing analogs of phosphate es ters, e.g., phosphorothioates, are becoming widely used as biochemical reagents [1,2]. Of particular relevance for this chapter are phosphate monoesters of serine, threonine, and tyrosine side chain -OH groups in polypeptides. Phosphorylation of these amino acid sides by protein ki nases and dephosphorylation by protein phosphatases represents a uni versal mechanism for biological regulation. The family of protein phos phatases that includes protein phosphatases 1 (PP1), 2A (PP2A), and 2B (PP2B or calcineurin) are metalloenzymes that can be activated by Mn2+. Protein phosphatase 2C (PP2C), although evolutionarily unre lated to the above phosphatases, is also activated by Mn2+. Despite the
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FIG. 1. Phosphate esters are one of the predominant forms of phosphorus in biological systems. Values for phosphoric acid acidity constants are from Smith and Martell [95].
