CRYSTALLOGRAPHIC STUDIES ON MALTOTETRAOSE-FORMING AMYLASE FROM ALCALIGENES SP. Jian-Hua Ma, Zi-Zheng Yan^#, Yao-Ping Wang, Yi Han, Ru-Chang Bi. Institute of Biophysics, Academia Sinica, Beijing 100101, P.R.China; ^#Institute of Microbiology, Academia Sinica, Shanghai 100080, P.R.China

Preliminary crystallographic study has been carried out with maltotetraose- forming amylase(E.C.3.2.1.60, G4-amylase), which was isolated and purified from Alcaligenes sp. found from Chinese soil. G4-amylase is a unique amylase which catalyzes the release of [[alpha]]-maltotetraose from the nonreducing ends of starch molecules. It is commercially important for producing maltotetraose with superior properties. This enzyme has molecule mass of about 60kD and pI4.45.

After an intensive screening of crystallization conditions was conducted with the enzyme, better G4-amylase crystals could be obtained using the hanging drop method with a drop consisting of 10mg/ml enzyme sample solution and equal volume of reservoir solution containing 0.1M Cacodylate buffer (pH6.5), 0.2M calcium acetate and 18% PEG-8000.

The G4-amylase crystals are orthogonal, and the unit cell has dimensions a=46.6Å, b=65.8Å and c=170.9Å and one molecule per asymmetric unit. 2.8Å intensity data have been collected with a G4-amylase crystal on Mar Research IP detector system in our laboratory. Further structure determination of G4-amylase is under way.