Effect of Co-expression of Vitreoscilla Hemoglobin on Expression of Β-mannanase in Pichia pastoris Expression of a Xylanase Gene Originated from Rumen Anaerobic Fungi Neocallimastix frontalis in Pichia pastoris Expression of Chicken Neurexophilin 1 Gene in Pichia pastoris Expression and Characterization of a Novel Mannanse From Achaetomium sp. Xz8 in Pichia pastoris The Influence of Spacer Peptide and C-Terminal His-tag on Activity and Secretion of MAT from Pichia pastoris