Enzyme activity (monoamine oxidase, histaminase, kallikreinogen) in carcinoids treated with parachlorophenylalanine
Fanciullacci, M.; Curradi, C.; Di-Lollo, F.; Sicuteri, F.
Bollettino della Societa Italiana di Biologia Sperimentale 51(17): 1025-1030
1975
ISSN/ISBN: 0037-8771 PMID: 130150 Document Number: 85828
The biological effects of p-chlorophenylalanine (PCPA), an inhibitor of serotonin (5-hydroxytryptamine, 5-HT) synthesis, were studied in 2 patients with carcinoid tumors. Platelet monoamine oxidase (MAO) activity, histaminase, soluble aminooxidases, kallikreinogen and plasma kallikrein inhibitor were evaluated after PCPA treatment. Platelet MAO activity and plasma aminooxidases were determined by using 14C-benzylamine and tyramine as substrates. Enzyme activity was calculated as maximum velocity (Vm) and the apparent affinity constant (Km). Kallikreinogen and plasma kallikrein inhibitor were determined by the kaolin contact technique. Platelet MAO activity showed a lesser benzylamine affinity in carcinoid tumor patients, and the Vm benzylamine/Vm tyramine ratio was reduced. PCPA treatment restored this ratio to normal, along with the affinity for the 2 substrates used. Plasma esterase activity was reduced after kaolin contact, indicating low kallikreinogen and kallikrein inhibitor levels.