Dietary Determinants Of Efficacy

At least four dietary factors can modulate phytase efficacy. First, high levels of dietary calcium or calcium/ phosphorus ratios reduce the effectiveness of phytase. In phytase-supplemented diets, the recommended calcium/ phosphorus ratio is 1.2:1, not 2:1 as used in diets with adequate inorganic phosphorus added. Second, moderate to high levels of inorganic phosphorus may inhibit the full function of phytase. Third, supplemental organic acids such as citric acid or lactic acid enhance phytase efficacy. Those acids may reduce the pH of stomach digesta, thus providing a better environment for phytase to function, and/or to enhance the solubility of digesta phosphorus and modify the transit time of digesta in the small intestine.

Table 1 Biochemical properties of phytases currently available for use in animal diets

Origin pH Temperature optimum optimum (°C)

Kcat

Kcat/Km

A. niger PhyAc'd'e'f

A. niger PhyBg A. fumigatus PhyAe'h'ij'k P. lyciil'm

E. coli AppAhi'n' o 'p ' w Bacillus sp.q'r's'l'u Wheatv'w

55 60 63

58 70 50 55 55 60

55 65

4.94

38 47

47 65

228 300

628 46 2200

"The values in parentheses are calculated after deglycosylation of proteins or based on the deduced peptide sequence. The value shown for A. niger phyB is the molecular mass of the tetramer. The molecular mass of the monomer is shown within parentheses.

bOnly phytic acid (IP6) is used as the substrate for all enzymes except for E. coli AppA. Assay conditions are as follows: A. niger PhyA: 58°C ' pH 5.0;

a. niger PhyB: 63°C ' pH 2.5; A. fumigatus PhyA: 58°C ' pH 5.0; P. lycii: 58°C ' pH 5.0; E. coli AppA: 35 37°C ' pH 4.5; Bacillus sp: 37°C ' pH 7.0;

cUllah et al. (1999) Biochem. Bioph. Res. Co. 264: 210 206.

dHan et al. (1999) Appl. Environ. Microbiol. 65: 1915 1918.

eUllah et al. (2000) Biochem. Bioph. Res. Co. 275: 279 285.

fUllah et al. (2002) Biochem. Bioph. Res. Co. 290: 1343 1348.

gUllah AHJ and Sethumadhavan K (1998) Biochem. Bioph. Res. Co. 243: 458 462.

hWyss et al. (1999) Appl. Environ. Microbiol. 65: 359 366.

iWyss et al. (1999) Appl. Environ. Microbiol. 65: 367 373.

jMullaney et al. (2000) Biochem. Bioph. Res. Co. 275: 759 763.

kRodriguez et al. (2000) Biochem. Bioph. Res. Co. 268: 373 378.

lLassen et al. (2001) Appl. Environ. Microbiol. 67: 4701 4707.

mUllah AHJ and Sethumadhavan K (2003) Biochem. Bioph. Res. Co. 303: 46 468.

nGreiner et al. (1993) Arch. Biochem. Biophys. 303: 107 113.

oGolovan et al. (2000) Can. J. Microbiol. 46: 59 71.

pRodriguez et al. (2000) Arch. Biochem. Biophys. 382: 105 112.

qKerovuo et al. (1998) Appl. Environ. Microbiol. 64: 2079 2085.

rKim et al. (1998) FEMS Microbiol. Lett. 162: 185 191.

uTye et al. (2002) Appl. Microbiol. Biotechnol. 59: 190 197.

vPeers (1953) Biochem J. 53: 102 110.

In addition' organic acids may release cations chelated by phytate; reducing the amount of insoluble phytate cation complexes that are resistant to phytase action thereby increasing the efficacy of endogenous or supplemented phytase. Last; inclusion of hydroxylated chole-calciferol compounds has been shown to improve dietary phosphorus and zinc utilization by chicks in an additive manner with phytase. Supplementing different phytases in combination has not shown any benefit over the singular additions. However adding phytase with other hydrolytic enzymes seems to produce a synergism. Furthermore there are several physical forms of phytase: powder granule and liquid. The chemical coating of phytase to improve heat stability may somewhat compromise its release in stomach.

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