Yeast alcohol dehydrogenase (YADH) solubilized in reverse micelles of aerosol OT (i.e., AOT or sodium bis (2-ethyl hexyl) sulfosuccinate) in isooctane has been shown to be catalytically more active than that in aqueous buffer under optimum conditions of pH, temperature, and water content in reverse micelles. Studies of the secondary structure conformational changes of the enzyme in reverse micelles have been made from circular dichroism spectroscopy. It has been seen that the conformation of YADH in reverse micelles is extremely sensitive to pH, temperature, and water content. A comparison has been made between the catalytic activity of the enzyme and the alpha -helix content in the conformation and it has been observed that the enzyme is most active at the maximum alpha -helix content. While the beta -sheet content in the conformation of the entrapped enzyme was found to be dependent on the enzyme-micelle interface interaction, the alpha -helix and random coil conformations are governed by the degree of entrapment and the extent of rigidity provided by the micelle core to the enzyme structure.