Microbial pro-transglutaminase (pro-MTGase) from Streptomyces mobaraensis was expressed in Pichia pastoris (Komagataella phaffii) under the control of constitutive GAP promoter. The single copy of the gene containing clone was grown in shake flasks to determine the optimum conditions for the production of recombinant proMTGase. Three temperature (20 degrees C, 25 degrees C, 28 degrees C) and four pH (5, 6, 7, 7.5) values were evaluated at the shake flask level for the extracellular production of pro-MTGase. The highest enzyme activity was obtained with low temperature (20 degrees C) and high pH (7.5). The maximum yield was 9120 U/L. For the large-scale extracellular production of pro-MTGase, the clone was cultivated in 5 L bioreactor. The fermentation process was carried out at 20 degrees C, pH 7 and 20% dissolved oxygen for 79 h. The enzyme activity was calculated as 37640 U/L for large-scale production. These results indicate that P. pastoris expression system is very suitable for recombinant MTGase production under the control of the GAP promoter.