Expression of A and B types of monoamine oxidase in neuroblastoma hybrid cells.

Monoamine oxidase (MAO) activity towards kynuramine as substrate was measured in 6 hybrid cells derived by fusion of neuroblastoma and glioma, liver or brain cells, and was compared with that of parental or non-parental clones. Activities varied from the lowest level of less than 0.15 pmol/min/mg protein in a neuroblastoma clone NB2A to the highest level of 127 pmol/min/mg protein in NCB20 mouse neuroblastoma x Chinese hamster embryo brain hybrid cells. The relative proportions of A and B types of MAO activities were determined in homogenates of each cell line by inhibition curves with clorgyline and deprenyl. Although the A type activity was found in all cell lines measured, MAO A was predominant in 9 clones, except for NCB20 hybrid cells, N4G-B-a neuroblastoma x glioma hybrid cells, and G8-1 myoblast. The ratio of type A/type B activity in NCB20, N4G-B-a and G8-1 cells was 20/80, 75/25 and 95/5, respectively. The results suggest that NCB20 cells are highly enriched in MAO type B, and that the NCB20 cell is an excellent model for studying the type B activity found in the brain in vivo.