Cysteinesulfinic acid decarboxylase activity in the mammalian nervous system: absence from axons

The activity of cysteinesulfinic acid decarboxylase (CSAD, EC 4.1.1.29) in extracts of liver of seven mammals varied greatly, whereas in extracts of brain from the same species, the variation was less marked. CSAD activity was readily measured in extracts of spinal cord from the same species, except those from rhesus monkey and man. The most noteworthy observation was the complete absence of CSAD activity in extracts of optic nerves and of sciatic nerves from all seven mammals. This suggests that taurine biosynthesis does not occur within axons and that intraaxonal taurine is supplied by axonal transport from the cell body.