Gamma-ray directional correlation study of bovine carbonic anhydrase

Abstract

Two perturbed gamma-gamma directional correlation experiments have been performed to examine internal fields and correlation times for the active region and active site in bovine carbonic anhydrase (BCA-B). A sample of BCA-B with 133Ba implanted in the active region was prepared and time-dependence of the anisotropy of the 356–81 keV cascade of 133Cs was measured at room temperature. Time-differential and time-integrated behavior of the perturbation factor indicates a possible time-dependent interaction with a relaxation constant λ22 = 5×107 sec−1. Using a previously reported value of rotational correlation time of BCA-B, the perturbation factor is found to be caused by a time-dependent electric quadrupole interaction with an electric field gradient having a time-averaged value of 1 V/Å2 at the nuclear site of 57Co. In a second experiment, BCA-B was demetallated and the zinc ion at the active site replaced by 57Co with no appreciable loss of specific activity. Time-differential measurements of the anisotropy of the 122–14 keV case in 57Fe showed that the anisotropy goes rapidly to zero. The time-integrated perturbation factor gives λ22 = 7×107 sec−1 at the active site.

Gamma-gamma directional correlation study of model membranes

“…The theory of PDC has been reviewed extensively (Frauenfelder and Steffen, 1966), and applications to biophysical systems have been previously reported (Liepert et al, 1968;Meares et al, 1969;Graf et al, 1974;Richer et al, 1974). If a radioactive nuclide decays by a gammagamma cascade, we may define the directional correlation function, W(O), as the relative probability that the second gamma photon is emitted at some angle 0 with respect to the direction of emission of the first photon.…”