Changes in the properties of honeybee haemolymph α-glucosidases following dithiothreitol dissociation of native complexes

Abstract

1. 1. The higher relative molecular mass ( M r ) forms of larval honeybee haemolymph α-glucosidases are dissociated by dithiothreitol (DTT) into lower M r electrophoretic forms, without any important loss of activity. 2. 2. The maximum velocity remains unchanged and the apparent dissociation constant is slightly increased, with K i ≅ 247 mM and I 50 ≅ 730 mM. 3. 3. By contrast, the major changes affect the Hill coefficient which decreases from 1.0 in controls to 0.7 in presence of 600 mM DTT. 4. 4. In the absence of both DTT and substrate, the major native enzyme form, isolated by gel filtration, spontaneously rearranges to give three additional minor forms, one of lower M r and two of higher M r . 5. 5. These data are consistent with the hypothesis of substrate-directed aggregation of enzyme protomers into functional complexes.