Purification and Characterization of Acidic Chitinases from Gizzards of Broiler (Gallus gallus L.)

Abstract

Acidic chitinases from the gizzards of a broiler were purified to homogeneity, using precipitation with $(NH_{4})_{2}SO_{4}$, ion exchanger chromatography, gel filtration, chromatofocusing and hydrophobic interaction chromatography. The enzymes, GAC1 and GAC2, were purified 180- and 194- folds with a recovery of 4.9% and 2.7%, respectively. The molecular mass of GAC1 and GAC2 were 48.2 kDa and 57.8 kDa, respectively. Chromatofocusing resulted in a pI of 3.1 for both enzymes. The purified enzymes were endochitinases that were devoid of ${\beta}-N-acetylglucosaminidase$ and lysozyme activity. Kinetic studies using $[^3H]chitin$ indicate that GAC1 has a $K_m$ and $V_{max}$ of 1.97 mg/ml and 185 mg/mg protein/h, respectively. The GAC2 has a $K_m$ and $V_{max}$ of 0.42 mg/ml and 92.3 mg/mg protein/h, respectively at optimal pH and temperature (pH 5.0 and $60^{\circ}C$). When the pentamer and hexamer of N-acetylglucosamine (GlcNAc) were used as a substrate, the major product by GAC1 was the dimer of GlcNAc with a differential accumulation of the monomer and trimer, depending upon the substrate. However, the GAC2 produced the dimer and trimer in an equal quantity, regardless of the substrate used. The first 9 $NH_2-terminal$ amino acid residues of the purified gizzard chitinase GAC1 and GAC2 shared a 100% homology. The first 25 $NH_2-terminal$ amino acid residues of GAC1 also shared 55-60% homology with animal chitinases and some animal proteins, such as whey protein and oviduct-specific proteins. However, little homology was found with either microbial and plant chitinases, or egg white lysozyme.

Keywords

• Broiler;
• Chitinase;
• Gizzards;
• $NH_2$-terminal;
• Purification