Rapid axonal transport of tyrosine hydroxylase in rabbit sciatic nerves

Stephen Brimijoin, Mary Jo Wiermaa

Research output: Contribution to journalArticle

23 Scopus citations

Abstract

We compared the axonal transport of tyrosine hydroxylawe with that of dopamine-β-hydroxylase by means of an in vitro stop-flow technique. Proximal to a locally cooled nerve region, the activity of both enzymes increased linearly for 3 h. Internal standards of partially purified adrenal enzyme showed that the increased activity of tyrosine hydroxylase was not due to changes in activators or inhibitors. Furthermore, this increased activity represented increased Vmax, unaccompanied by changes in Km for tyrosine; probably, therefore, it reflected increased concentrations of the enzyme. From the rates of increase of enzyme activity, we calculated that, on the average, tyrosine hydroxylase was transported at 0.78 mm/h, and dopamine-β-hydroxylase at 2.4 mm/h. Much less tyrosine hydroxylase than dopamine-β-hydroxylase seemed free to move in the nerves, suggesting greater similarity between true transport velocities than between average velocities of these enzymes. When nerves were rewarmed after local cooling for 3 h, waves of accumulated enzyme activity moved distally. The wave of dopamine-β-hydroxylase activity had a single peak moving at about 14 mm/h. The wave of tyrosine hydroxylase activity had a small component moving this fast, but more of it moved slower, at velocities down to 5 mm/h. Although tyrosine hydroxylase was apparently much more soluble than dopamine-β-hydroxylase there was no evidence that the rapidly transported fraction of either enzyme had a different subcellular distribution from that of slower transported or stationary fractions.

Original languageEnglish (US)
Pages (from-to)77-96
Number of pages20
JournalBrain Research
Volume121
Issue number1
DOIs
StatePublished - Jan 31 1977

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology

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