The presence of 2′, 3′‐cyclic AMP 3′‐phosphohydrolase in glial cells in tissue culture

T he E nzyme 2′, 3′‐cyclic AMP 3′‐phosphohydrolase (CNP) is regarded as a marker for myelin (KURI‐ HARA and MANDEL, 1970) on the basis of its regional and subcellular distribution (K urihara and T sukada , 1967), its ontogenetic characteristics (KURIHARA and TSUKADA, 1968), and its behaviour in two strains of myelin‐deficient mutant mice (K urihara , N ussbaum and M andel , 1969). However we have isolated highly‐purified preparations of neuronal plasma membrane from rat brain synaptosomes which contain this enzyme activity (M organ , W olfe , M andel and G ombos , 1971). Two explanations of this finding are possible. The activity could be due to the presence of myelin, but this explanation is ruled out by electron microscopy and by the low level of cerebrosides in the synaptosomal plasma membrane preparations. Myelin is extremely rich in cerebrosides ( norton and A utilio , 1966). The second possibility is that the enzyme, 2′, 3′‐cyclic AMP 3′‐phosphohyrolase, may also be found in the glial cells from which myelin is derived (B unge , B unge and P appas , 1962). To test our hypothesis that 2′, 3′‐cyclic AMP 3′‐phosphohydrolase is not a specific marker for myelin, but is also found, in glial cells, we have examined a tumoral glial cell line maintained in myelin‐free tissue culture.