In phosphatase

Saha S, Mina BL, Gopinath KA, Kundu S, Gupta HS (2008b) Relative changes in phosphatase activities as influenced by source and application rate of organic composts in field crops. Biores Technol 99 1750-1757... 

Reactivation of alkaline phosphatase is of considerable practical significance since regulatory tests for pasteurization assume the absence of phosphatase activity. An official AOAC method used to distinguish between renatured and residual native alkaline phosphatase is based on the increase in phosphatase activity resulting from addition of Mg2 + the activity of renatured alkaline phosphatase is increased about 14-fold but that of the native enzyme is increased only two-fold. 

Many aminopeptidases are metalloenzymes.437 Most studied is the cytosolic leucine aminopeptidase which acts rapidly on N-terminal leucine and removes other amino acids more slowly. Each of the subunits of the hexameric enzyme contains two divalent metal ions, one of which must be Zn2+ or Co2+438/439 A methionine aminopeptidase from E. colt contains two Co2+ ions440/441 and a proline-specific aminopeptidase from the same bacterium two Mn2+.442 In all of these enzymes the metal ions are present as dimetal pairs similar to those observed in phosphatases and discussed in Section D,4 and to the Fe-Fe pairs of hemerythrin and other diiron proteins (Fig. 16-20). A hydroxide ion that bridges the metal ions may serve as the nucleophile in the aminopeptidases.438 A bound bicarbonate ion may assist.4383... 

Reid, M.S. Bieleski, R.L. (1970). Changes in phosphatase activity in phosphorus-deficient spirodela. Planta 94, 273-81. 

Koike T, Kimura E (1991) Roles of zinc(II) ion in phosphatases - a model study with zinc(II) macrocyclic polyamine complexes. J Am Chem Soc 113 8935-8941... 

J. Miiller, B. Westenberg, T. Boiler and A. Wiemken (1992). Synthesis and degradation of polyphosphate in the fission yeast Schizosaccharomyces pombe mutations in phosphatase genes do not affect polyphosphate metabolism. FEMS Microbiol. Lett., 71, 151-156. 

The abnormal phosphorylation of tau associated with AD may be related to either an increase in kinase activity (glycogen synthase kinase 3P, cyclin-dependent kinase-5, p42/44 MAP kinase, p38 MAPK, stress-activated protein kinases, mitotic protein kinases) or a decrease in phosphatase activity (protein phosphatases 1, 2a, 2b), suggesting soluble tau as a cause of neuronal degeneration (Buee et al., 2000 Tian and Wang, 2002 Chen et al., 2008 Liu et al., 2008 Yang et al., 2008 Zhou et al., 2008a). 

In addition, potentially multidentate ligands like proteins (theoretically, nd > 100) will accomodate several identical or different metal ions during metallization, and there are cases in which differently highly metal-ion-loaded metalloproteins will fulfill the same or very similar catalytic functions, e.g. in phosphatases... 

Fig. 2.20 Formal fitness landscape of various biocatalytic and inactive (i.e., the latter being located outside the window of essentiality ) metal ions for the carboxypeptidase A (Vallee and Williams 1968). The enzyme reconstituted by cobalt (treatment with EDTA, then addition of Co +) is considerably more active than the native Zn version , while Cd (and other ions) afford poorly to non-active metalloproteins in this case. (Relative) catalytic turnover rates are from Vallee and Williams 1968, x and c values this work and previous publications by this author. Here, sufficient abundance of the corresponding ions is taken for granted owing to in-vitro addition to apoprotein, so c k is not hmited by c, but merely represents the catalytic features pertinent to k, obtained from either biochemistry (several metal ions being present, e.g. in phosphatases) or experiments with reconstituted apoproteins...

The second protein, phosphatase inhibitor-1, regulates protein phosphatases during glycogen metabolism once it has been activated by a cAMP-dependent protein kinase. The phosphorylated site in phosphatase inhibitor-1 is a threonine residue, and this is preceded by the sequence Arg-Arg-Arg-Arg-Pro. Another protein that is activated by phosphorylation by a cAMP-dependent kinase is phenylalanine hydroxylase, although the site of the phosphorylation has not been determined. 

H25. Hunsberger, A., and Ferguson, L. K., Variations in phosphatase and inorganic phosphorus in serum during fracture repair. Arch. Surg. 24, 1052-1060 (1932). 

FIGURE 3 Effect of changes in phosphatase rate on the steady-state relation between force and phosphorylation in swine carotid artery according to the Hai and Murphy four-state model. The rate constants for phosphatase activity (kj and k ) were varied over a 50-fold range from 0.1 s (dotted line) to 5 s (dashed line). The rate constants for kinase activity (kj and k ) were varied to produce the desired range of phosphorylation. All other constants (kj and k4, and ky) were consistent with the original Hai and Murphy formulation. 

As pointed out by Butler et al. (1994), the a-toxin-permeabilized preparation used by Kitazawa et al. might contain endogenous phosphatase inhibitors that have been lost in the Triton-skinned preparation. This could at least partially explain the observed difference in phosphatase rate, and is an intriguing possibility relating to the demonstration that receptor agonists are able to increase Ca2+ sensitivity in neuroeffector-coupled permeabilized preparations by a mechanism involving inhibited myosin light chain phosphatase (MLCP) activity (Kitazawa et al., 1991 Kubota et al.,... 

Two distinct types of binding sites in phosphatase can be distinguished on the basis of their diflFerential aflSnity for cobalt and zinc. The restoration of activity upon addition of increments of zinc to the apo-enzyme is compared with the activity resulting from addition of similar increments of cobalt in Figure 3. Notably, the first 2 gram atoms of zinc restore nearly all the activity of native phosphatase the last two zincs bound have httle eflFect on it. 

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