... Yamashita E, Yamamoto M, Kumasaka T, Ueki T, Nanba H, Ikenaka Y, Takahashi S, Sato M et al (2000) Crystal structure of N-carbamyld-amino acid amidohydrolase with a novel catalytic framework common ... of the bar indicates the fraction assayed (B) Reducing SDS ⁄ PAGE of the active fraction showed a characteristic nitrilase band of 40 kDa The contaminating band at 60 kDa was identified as GroEL ... end of each chromatographic step, the active protein was investigated by negative-stain electron microscopy Assay for enzyme activity Nitrilase activity was analysed by assaying the release of ammonia...