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Assignment of A and B Types of Monoamine Oxidase in NCB20 Hybrid Cells to Those of the Parental Cells by Peptide Mapping

Abstract: The structures of [3H]pargyline‐labeled, flavin‐containing polypeptides of monoamine oxidase (MAO) from hybrid NCB20 cells, and their parental cells, A/J mouse brain cells and Chinese hamster brain cells, were analyzed and compared by using sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE), and limited proteolysis and one‐dimensional peptide mapping in SDS gels. After preincubation of mitocnondrial preparations with deprenyl or clorgyline, the flavin‐containing polypeptide of type A or type B MAO was selectively labeled with [3H]pargyline. SDS‐PAGE of [3H]pargyline‐labeled mitochondrial samples revealed that the polypeptide with apparent Mr of 62,000 was associated with type A activity in the three types of cells, and that the polypeptide with apparent Mr of 61,000 or 58,000 was associated with type B activity in Chinese hamster brain cells and NCB20 cells or A/J mouse brain cells, respectively. Chymotrypsin digestion of the [3H]pargyline‐labeled polypeptides and the peptide mapping in SDS gels from A/J mouse and Chinese hamster brain cells produced identical map patterns between the two type A MAOs, almost the same map patterns (with the exception of one additional peptide fragment) between the two type B MAOs, and different map patterns between type A and type B MAOs. The results of identical treatments of the [3H]pargyline‐labeled polypeptides of MAOs in NCB20 cells showed that type A and type B MAO in NCB20 cells were similar to type A MAO of A/J mouse and Chinese hamster brain cells and to type B MAO of Chinese hamster brain cells. We previously reported that the activity of type A MAO in NCB20 cells coincided with the activity of MAO in N18TG‐2 neuroblastoma cells which originate from A/J mouse and express solely type A MAO activity. Previous karyological studies indicated that most chromosomes of NCB20 cells derived from A/J mouse and that chromosome X, which may contain type A MAO of Chinese hamster origin, could not be recognized in NCB20 cells. The present study and these previous findings indicate that type A and type B MAOs in NCB20 cells may originate from A/J mouse and Chinese hamster, respectively, and that type A and type B MAO activities may be associated with distinct enzyme molecules.