Changes in the properties of honeybee haemolymph alpha-glucosidases following dithiothreitol dissociation of native complexes.
1. The higher relative molecular mass (M(r)) forms of larval honeybee haemolymph alpha-glucosidases are dissociated by dithiothreitol (DTT) into lower M(r) electrophoretic forms, without any important loss of activity. 2. The maximum velocity remains unchanged and the apparent dissociation constant is slightly increased, with Ki approximately equal to 247 mM and I50 approximately equal to 730 mM. 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. 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. These data are consistent with the hypothesis of substrate-directed aggregation of enzyme protomers into functional complexes.
Debevec
M
M
Faculty of Veterinary Medicine, Department of Biology, Belgrade, Yugoslavia.
Bounias
M
M
Popeskovic
D
D
D000818:Animals; D001516:Bees / Q000737:chemistry*; D004229:Dithiothreitol / Q000494:pharmacology*; D006458:Hemolymph / Q000201:enzymology*; D007700:Kinetics; D008970:Molecular Weight; D000520:alpha-Glucosidases / Q000737:chemistry*
D000520:alpha-Glucosidases; D004229:Dithiothreitol