2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase A) is a phosphodiesterase that catalyzes the following reaction: Nucleoside 2',3'-cyclic phosphate + H2O = nucleoside 2'-phosphate. CNPase is present in very high levels in brain and peripheral nerve. This enzyme is found almost e, Xenopus/Amphibian,clusively in oligo-dendrocytes and Schwann cells, the cells that form myelin in the central and peripheral nervous system, respectively. Therefore, CNPase has been very useful as a marker for these particular cell types.