palavras-chave Activity Bacterial Proteins Biocatalysis Endo-1,4-beta Xylanases Enzyme Stability Glycoside Hydrolases Glycoside hydrolase family 8 Hydrogen-Ion Concentration Kinetics Protein Engineering Protein Structure, Tertiary Pseudoalteromonas Solubility Spectrometry, Fluorescence Stability Xylanase pH dependence