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KINETIC STUDIES ON THE DIMERIC MYOGLOBIN FROM BUSYCON CANALICULATUM AND THE POLYMERIC HEMOGLOBIN FROM LUMBRICUS TERRESTRIS
Abstract
Busycon myoglobin had been reported to be slightly cooperative in binding oxygen. Preliminary flash-photolysis studies on the CO-ligated protein in this laboratory had showed no evidence of a quickly-reacting form. Oxygen equilibrium measurements and kinetic studies at pH 7 performed on ammonium sulfate fractionated and non-fractionated Busycon myoglobin samples showed no significant differences attributable to the method of preparation. Oxygen equilibrium studies showed that Busycon myoglobin is virtually non-cooperative with a Hill number not significantly different from one. Laser photolysis measurements showed no evidence for a quickly-reacting form. Kinetic light-scattering studies of the alkaline dissociation of Lumbricus hemoglobin (MW 3 x 10('6)) allowed us to determine concentrations of intermediates as a function of time. Divalent cations stabilize the dodecamer (3 x 10('6) MW) at pH 10.3. Kinetic studies show evidence for 3 conformational domains: (rho)--a domain that is always high affinity R-state; (sigma) and (tau)--domains that can undergo R--S and R--S--T conformational changes, respectively. Relaxation experiments suggest CO-O(,2) ligand inequivalence for Lumbricus erythrocruorin. At pH 10.3, kinetic measurements show a shift toward the higher affinity R and S forms. In CO association, the apparent populations of (sigma) (25%) and (tau) (50%) domains at pH 7 for the dodecamer and protomer forms are reversed at pH 10.3. Oxygen and CO association rate constants for the dodecamer and protomer forms increased at least 2-fold from pH 7 to 10.3. Oxygen and CO association rate constants for the dodecamer and protomer forms increased at least 2-fold from pH 7 to 10.3. Oxygen dissociation rate constants (k and k*) decreased significantly for both the dodecamer and the protomer when the pH was increased from 7 to 10.3. The shift toward the higher affinity R and S forms reflect fewer structural constraints at alkaline values of pH.
Subject Area
Biochemistry
Recommended Citation
SCHREIBER, JANE K, "KINETIC STUDIES ON THE DIMERIC MYOGLOBIN FROM BUSYCON CANALICULATUM AND THE POLYMERIC HEMOGLOBIN FROM LUMBRICUS TERRESTRIS" (1983). ETD collection for University of Nebraska-Lincoln. AAI8404847.
https://digitalcommons.unl.edu/dissertations/AAI8404847