LOCAL CHANGES IN SUBCELLULAR DISTRIBUTION OF DOPAMINE‐β‐HYDROXYLASE (EC 1.14.2.1) AFTER BLOCKADE OF AXONAL TRANSPORT

Abstract— The distribution of DBH activity between soluble and sedimentable fractions of hypotonic homogenates was examined in rat sympathetic ganglia and nerves after interruption of axonal transport. Local application of colchicine to superior cervical ganglia caused an increase mainly in particulate DBH activity, which was presumably bound to membranes. Likewise, in sciatic nerves, particulate DBH activity accumulated on both sides of a ligature and disappeared from a region well below a ligature much faster than did soluble activity. On the other hand, 18 h after simultaneous application of two ligatures to the nerve, neither total DBH activity nor subcellular distribution of this activity changed in the isolated nerve region. More detailed analysis showed that ligation affected the distribution of DBH activity within a fraction that sedimented at 140,000 g after homogenization of nerves in isotonic sucrose. Just above a ligature, osmotically releasable DBH activity was a smaller proportion of the sedimentable activity than in control nerves. However, as compared to controls, osmotically releasable DBH activity was a larger proportion of the activity in the sedimentable fraction from a region well below a ligature. A model was developed which accounts for some of these results by postulating that DBH is associated with different compartments in sciatic nerve which have different rates of transport and different proportions of soluble and bound enzyme.