Distribution of three isozymes of brain enolase (2-phospho- d-glycerate hydro-lyase, EC 4.2.1.11) (αα, αγ and γγ forms) in clonal cell lines of neuroblastoma (NS20Y and N18TG-2), glioma (C6BU-1), and hybrid cells (NG108-15, NCB20, Nbr10A, Nbr20A, N4G-B-a and N4G-C-a) was examined with a sensitive enzyme immunoassay system, that uses a rabbit antibody to rat brain enolase αα or γγ. All cell lines tested were found to possess the enolase which contains γ subunit (a neuro-specific protein), although the αα enolase (non-neuronal enolase) was the dominant form in these cells. A clonal rat glioma (C6BU-1) cell contained about 40, 1 and 0.07 μg/mg protein of αα, αγ and γγ enolases, respectively, at the confluent stage. Inclusion of 1 mM dibutyryl cyclic AMP or 10 μM prostaglandin E 1 plus 1 mM theophylline in the culture medium of a hybrid cell (NG108-15, mouse neuroblastoma x rat glioma) resulted in a more than 2-fold increase in the concentrations of αγ and γγ in the cell within a few days, with little change in the αα enolase concentration. A similar increase in the concentration of γ subunit by the nucleotide (but not by prostaglandin E 1 plus theophylline) was also observed in the glioma cell (C6BU-1) line. The results suggest that the γ subunit or the neuron-specific protein can be regulated in NG108-15 and C6BU-1 cells in a cyclic AMP-dependent fashion.
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