Retrograde alteration of 6-phosphogluconate dehydrogenase in axotomized superior cervical ganglia of the rat

Human brain 6-phosphogluconate dehydrogenase: purification and kinetic properties

6-Phosphogluconate dehydrogenase has been purified from human brain to a specific activity of 22.8 U/mg protein. The molecular weight was 90,000. At low ionic strengths enzyme activity increased, due to an increase in Vmax and a decrease in Km for 6-phosphogluconate, and activity subsequently decreased as the ionic strength was increased (above 0.12). Both 6-phosphogluconate and NADP+ provided good protection against thermal inactivation, with 6-phosphogluconate also providing considerable protection against loss of activity caused by p-chloromercuribenzoate and iodoacetamide. Initial velocity studies indicated the enzyme mechanism was sequential. NADPH was a competitive inhibitor with respect to NADP+, and the Ki values for this inhibition were dependent on the concentration of 6-phosphogluconate. Product inhibition by NADPH was noncompetitive when 6-phosphogluconate was the variable substrate, whereas inhibition by the products CO2 and ribulose 5-phosphogluconate and NADP+ were varied. In totality these data suggest that binding of substrates to the enzyme is random. CO2 and ribulose 5-phosphate are released from the enzyme in random order with NADPH as the last product released.

Early rapid and transient increase in ornithine decarboxylase activity within sympathetic neurons after axonal injury

The activity of ornithine decarboxylase (ODC) was examined in the rat superior cervical ganglion during development and after postganglionic axotomy. During development the enzyme activity in the ganglion was transiently elevated at 19 days gestation (2 days before birth) and then declined to low adult activities by 5 days after birth. After axotomy the enzyme activity in the ganglion was rapidly increased. As early as 2 h after the injury the activity was increased to 200% and by 10 h it attained a peak of 453% above control values. The activity then rapidly declined to a lower value of about 200% above control by 24 h, where it remained as long as 5 days and then returned to control values by 10 days postoperative. The early increase in ODC activity was demonstrated by inhibitor cytochemistry to occur within neuronal cell bodies. The ODC activity was also increased after preganglionic nerve transection (denervation) (275%), end organ removal (60%), and 6-hydroxydopamine treatment (75%). We conclude that increased ODC activity is one of the earliest events in the reaction of the nerve cell body to axonal injury, and that increased ODC activity is a common feature of drastic metabolic alterations in neurons of the superior cervical ganglion.