en 23408781 Human alpha 1-antitrypsin (AAT) cDNA was obtained from HepG2 cell lines. After PCR and construction of expression vector pPICZα-AAT, human AAT was expressed in the yeast Pichia pastoris (P.pastoris) in a secretary manner and under the control of inducible alcohol oxidase 1 (AOX1) promoter. The amount of AAT protein in medium was measured as 60 mg/l 72 hr after induction with methanol. Results indicated the presence of protease inhibitory function of the protein against elastase. Purification was done using His-tag affinity chromatography. Due to the different patterns of glycosylation in yeast and human, the recombinant AAT showed different SDS-PAGE patterns compared to that of serum-derived AAT while pI shifted from 4.9 in native AAT compared to 5.2 in recombinant AAT constructed in this study. Alpha 1-antitrypsin, Pichia Pastoris, Protease inhibitors, Recombinant proteins 127 134 https://www.ajmb.org/En/Article.aspx?id=66 https://www.ajmb.org/PDF/En/FullText/66.pdf SarehArjmandSchool of Pharmacy, Zanjan University of Medical Science, Zanjan, Iran244ElhamBidramDepartment of Clinical Biochemistry, Tarbiat Modares University, Tehran, Iran245AbbasSahebghadam LotfiDepartment of Clinical Biochemistry, Tarbiat Modares University, Tehran, Iran246MehdiShamsaraNational Institute of Genetic Engineering and Biotechnology (NIGEB), Tehran, Iran247Seyed JavadMowlaDepartment of Molecular Genetics, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran248