Thermostable and alkalistable exopolygalacturonase of Bacillus pumilus dcsr1: Characteristics and applicability

The bioactive form of thermostable and alkali stable pectinase of Bacillus pumilus dcsr1 is a homodimer of the molecular mass of 60 kDa with a pI of 4.6. The enzyme is optimally active at 50 °C and pH 10.5, and its Michaelis constant (Km), maximum rate of reaction (V_max), activation energy (E_a), and temperature quotient (Q₁₀) values (for citrus pectin) are 0.29 mg mL^-1, 116 μmole mg^-1 min^-1, 74.73 KJmol^-1 and 1.57, respectively. The enzyme has a shelf life of one and a half years at room temperature as well as 4 °C. The activity of the enzyme is stimulated by Mn²⁺ and Ca²⁺ and inhibited by Hg⁺, Cd²⁺, Co²⁺, Zn²⁺, Fe²⁺, Pb²⁺, EDTA and urea to a varied extent. The conformational studies of the enzyme revealed a high β-sheet content in the bioactive dimer, and high α-helix in the inactive monomer. The Circular Dichroism (CD) spectra of the dimer in the presence of inhibitors suggested a marked decrease in β-sheet, and a significant increase in α-helix, suggesting a key role of β-sheets in the enzyme catalysis. Based on the end product analysis, the enzyme is an exopolygalacturonase with a unique ability of transglycosylation. When ramie fibers were treated with the enzyme, removal of gummy material (pectin) was visible, confirming its applicability in the degumming process.