Aromatic-L-amino-acid decarboxylase activity in mouse pancreatic islets.
Aromatic-L-amino-acid decarboxylase activity has been measured in intact or homogenised pancreatic islets of ob/ob mice (Umeå ob/ob). The method used involves the trapping and measuring of the 14CO2 released from L-[1-14C]dihydroxyphenylalanine (L-dopa). Islets showed a decarboxylase activity which was dependent on pyridoxal phosphate and inhibitable by 0.1 mM benserazide or 0.1 mM alpha-monofluoromethyldopa. Maximum activity in intact islets was about 330 mmol/kg dry islet per h with an apparent Km of 3.3 mM. Islet homogenates had a Vmax of about 120 mmol/kg per h with a Km of 0.3 mM. L-5-Hydroxytryptophan, m-tyrosine and o-tyrosine interfered with the decarboxylation of L-dopa in a way that suggested a high activity also towards those substrates. L-Phenylalanine, L-tyrosine and D-glucose had no effect. At 0.05 mM L-dopa islet homogenates showed a much higher activity than homogenates of liver, kidney, or spleen. Islet uptake of L-[3H]dopa was well in excess of the decarboxylation rate and thus probably not rate-limiting. It is concluded that mouse pancreatic islets have a high activity of aromatic-L-amino-acid decarboxylase. This is in accordance with previous suggestions of a stimulatory effect of this enzyme on insulin secretion.
D000818:Animals; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000378:metabolism*; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000201:enzymology*; D007980:Levodopa / Q000378:metabolism; D051379:Mice; D008820:Mice, Obese
D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D007980:Levodopa; D001142:Aromatic-L-Amino-Acid Decarboxylases