Studies on porphyrinogen carboxy-lyase from chick embryo liver

• Published in: Enzyme (Basel) Vol. 31; no. 2; p. 79
• Main Authors: Taira, M C, San Martín de Viale, L C
• Format: Journal Article
• Language: English
• Published: Switzerland 01-01-1984
• Subjects: Animals; Carboxy-Lyases - analysis; Carboxy-Lyases - metabolism; Chick Embryo; Edetic Acid - pharmacology; Glutathione - pharmacology; Hydrogen-Ion Concentration; In Vitro Techniques; Liver - enzymology; Oxygen; Temperature
• ISSN: 0013-9432
• DOI: 10.1159/000469507

The purpose of the present work was to find the optimal conditions for the assay of chick embryo liver porphyrinogen carboxy-lyase. The enzyme activity was studied as a function of protein and substrate concentrations, time, pH value and incubation temperature. The effects of reduced glutathione (GSH), ethylenediaminetetra-acetate (EDTA), oxygen and several chemical compounds such as pyridoxal phosphate, sodium and potassium halogenated salts, sulph - hydryl reagents, chelating agents and ferrous iron were also investigated. The following results were found: (1) The optimal protein concentration was 1.25-2.5 mg/ml. For the substrate uroporphyrinogen III, the best concentration was 2 mumol/l; a slight inhibition was found at higher substrate concentrations. (2) The optimal pH value was 6.8 for both stages of uroporphyrinogen III decarboxylation ( octacarboxylic first stage---heptacarboxylic second stage--- tetracarboxylic porphyrinogen). (3) The activity increased with the incubation temperature (25-60 degrees C). (4) The enzyme activity was not enhanced by the addition of GSH or other sulph - hydryl reagents (cysteine and dithiothreitol), nor by the incorporation of EDTA or other chelating agents (Na-diethyldithiocarbamate, alpha,alpha'-bipyridyl and Na-pyrophosphate). (5) Oxygen diminished the second stage of decarboxylation. (6) Pyridoxal phosphate seems not to be a cofactor necessary in the decarboxylation. (7) NaCl or KCl diminished the activity in higher degree than did NaF or KF; the second stage was, in all cases, more affected than the first. (8) FeSO4 slightly diminished the second stage of uroporphyrinogen III decarboxylation at concentrations of 0.05 and 0.15 mmol/l, but both stages were significantly decreased at 0.3 mmol/l.