Characterization of pancreatic islet monoamine oxidase.
Monoamine oxidase (MAO) is present in isolated islets of Langerhans of rabbits, golden hamsters, and rats. Tryptamine, tyramine, serotonin, and dopamine can serve as substrates for this enzyme. We compared the properties of islet and liver MAO in the rabbit. The Michaelis constant (K(m)) for tryptamine of islet MAO (6.5 times 10-5M) is greater than the K(m) of liver MAO (3 times 10-5M). The K(m) for tyramine of islet MAO (1.5 times 10-4M) is similar to the K(m) of liver MAO (1.8 times 10-4M). Islet MAO appeared to be more susceptible to heat inactivation (50 degrees C) than did liver MAO. This may be an artifact produced by the collagenase technique used in the preparation of the islets, as collagenase treatment of liver increased the thermal lability of the MAO in this tissue. Liver and islet MAO have a comparable sensitivity to MAO inhibitors such as clorgyline, deprenyl, tranylcypromine, pargyline, and harmine. The present report, along with previous reports that MAO inhibitors alter insulin secretion, suggests that islet MAO may modify insulin secretion.
D000818:Animals; D006224:Cricetinae; D004355:Drug Stability; D006358:Hot Temperature; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000201:enzymology*; D007668:Kidney / Q000201:enzymology; D008099:Liver / Q000201:enzymology; D008297:Male; D008995:Monoamine Oxidase / Q000378:metabolism* / Q000502:physiology; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D009928:Organ Specificity; D010179:Pancreas / Q000201:enzymology; D011817:Rabbits; D051381:Rats; D013045:Species Specificity; D013329:Structure-Activity Relationship; D014363:Tryptamines; D014439:Tyramine
D007328:Insulin; D008996:Monoamine Oxidase Inhibitors; D014363:Tryptamines; D008995:Monoamine Oxidase; D014439:Tyramine