Arginine residues alkaline phosphatase

Isolation of alkaline phosphatase from Escherichia coli in which 85% of the proline residues were replaced by 3,4-dehydro-proline affected the heat lability and ultraviolet spectrum of the protein but the important criteria of catalytic function such as the and were unaltered (12). Massive replacement of methionine by selenomethionine in the 0-galactosidase of E. coli also failed to influence the catalytic activity. Canavanine facilely replaced arginine in the alkaline phosphatase of this bacterium at least 13 and perhaps 20 to 22 arginyl residues were substituted. This replacement by canavanine caused subunit accumulation since the altered subunits did not dimerize to yield the active enzyme (21). Nevertheless, these workers stated "There was also formed, however, a significant amount of enzymatically active protein in which most arginine residues had been replaced by canavanine." An earlier study in which either 7-azatryptophan or tryptazan replaced tryptophan resulted in active protein comparable to the native enzyme (14). 

Rothman and Byrne 46) have used tryptic digestion to determine whether the subunits of alkaline phosphatase are identical. Since trypsin specifically cleaves at lysyl and arginyl residues, there will be as many peptides formed as there are arginine and lysine residues if the mono-... 

The AP from E. coli contains two Zn2+ ions and one Mg2+ ion in the active site.68,91 The Zn ions play the most direct roles in catalysis the Mg2+ has been suggested to function as the provider of the general base that deprotonates the Ser nucleophile, in the form of a Mg-coordinated hydroxide.98 All known alkaline phosphatases have this conserved three metal ion center, as well as an arginine residue (Arg-166 in E. coli AP) that plays a role in binding and probably in transition state stabilization (Fig. 18). 

---