Abstract: Tacrolimus(FK506)is a novel immunosuppressant.The results of the influence of amino acid on tacrolimus production show that the yield of tacrolimus are increased by about 59% by adding 2.5 g/L(isoleucine(Ile)) on the initial stage of fermentation,while the concentration of the propionoic acid is greatly increased and the activity of propionyl-CoA synthetase is achieved to 600 U/g in the production formation phase.The reason for the increase of tacrolimus titer is that the synthesis of propionyl-CoA and othe...