Characterization of monoamine oxidase isoforms in human islets of Langerhans

In this paper, we describe the characterization of the expression of monoam ine oxidase (MAO) in whole pancreas and in isolated islets of Langerhans fr om human. Classical monamine oxidase activity assays reveal that both isofo rms A & B are present in human pancreas. Two complementary approaches indic ated that both MAO A and B are expressed in isolated islet: RT-PCR using sp ecific primers revealed amplification products with the expected size for M AO-A and MAO-B: two peptides corresponding to MAO A (similar to 61 kDa) and B (similar to 55 kDa) were detected using a polyclonal anti MAO-A/MAO-B an tiserum. Western blotting and subsequent densitometric analysis indicate th at whole and endocrine pancreas express the two isoforms with different rel ative proportions. Islets appear to express almost twice as much MAO protei n as whole pancreas, in near equal proportions of the two isoforms, whereas whole pancreas expresses more MAO-A than the B isoform. The expression of MAO A and B in islets could be the first step toward the characterization o f the functional properties of these enymes in the endocrine pancreas.