Effect of ethanol on the stability and conformational changes of transglutaminase from Streptomyces hygroscopicus (MTGase) was studied. The presence of 10% ethanol increased 20% activity and about 85% activity was lost in 50% ethanol-aqueous solution after incubation for 60 min at 25 degrees C. The K-m and V-max of the enzyme were 63.13 mmol/L and 14.02 mu mol/(mg protein min) in the presence of 10% ethanol, and 34.20 mmol/L and 0.68 mu mol/(mg protein min) in the presence of 30% ethanol, respectively. The results of spectral determination indicated that MTGase did not undergo significant structural changes in 10% ethanol-aqueous solution. At ethanol concentration of 40%, the alpha-helix structure content of the enzyme decreased from 20.5 +/- 0.5% to 14.3 +/- 0.7% and the unordered structure content increased from 46.4 +/- 0.5% to 72.6 +/- 1.7%. Some polyhydroxy compounds could improve the stability of the enzyme at high ethanol concentration. (C) 2008 Elsevier Ltd. All rights reserved.