Alkaline phosphatase molecular properties

The most important aspect of the study of Co(II) metalloenzymes is the possibility of using the metal ion as a functional, built-in reporter of the dynamics of the active site. The spectral and magnetic properties of Co (II) carbonic anhydrase have given valuable clues to the catalytic function of this enzyme. The recent studies of Co(II) alkaline phosphatase and Co (II) carboxypeptidase A indicate the general applicability of this approach to enzymes where the probe properties of the constitutive metal ion are poor. The comparison of the absorption spectra of these enzymes and low-molecular weight models have shown that the proteins provide irregular, and in some cases nearly tetrahedral environments. It is obvious, however, that a knowledge of the crystal structures of the enzymes is necessary before the full potential of this method can be exploited. 

Francko and Heath (1979) studied the influence of UV radiation on the phosphate complexation properties of dissolved humic substances from Crazy Eddie Bog in the central United States. In this bog, filterable phosphorus compounds were largely associated with humic substances of high apparent molecular weight. These fulvic acid-phosphorus associations resisted hydrolysis by alkaline phosphatase, but released orthophosphate upon irradiation with low doses of UV radiation, " e turnover time of the fulvic acid-phosphorus compounds was calculated to be less than 1 hour at the surface of a lake on a cloudless day. 

Recent developments in the structural analyses of enzymes that cleave phosphate esters have revealed a common property for the reaction center (60, 81, 93, 130), namely, more than one metal ion, usually Zn, is involved. The first example of this kind to be identified was E. coli alkaline phosphatase, an isologous dimer of molecular weight 94,058, which contains 4.0 ( 0.3) g atoms of tightly bound Zn " per mole and 1.3 ( 0.2) g atoms of Mg- per mole (130). Recent refinements of the structure of this enzyme (93) containing PO ion show that two phosphate oxygen atoms... 

The alkaline phosphatase from calf intestinal mucosa (CIAP) has many catalytic properties in common with the BAP (see Section I,A, this chapter). CIAP is also a dimeric, Zn-metalloenzyme, but it has a slightly larger molecular size (130 kDa). One notable distinction is that CIAP is heat labile compared with BAP. This property alone makes the CIAP a valuable alternative to BAP in many applications requiring successive treatments with other enzymes. 

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