The relationship between the intraluminal Ca2+ content of endoplasmic reticulum and the rate of the glucuronidation of p-nitrophenol was investigated in isolated rat hepatocytes. Different agents which decrease the Ca2+ level in the endoplasmic reticulum [calcium ionophores (A23187, ionomycin) or Ca2+-ATPaseinhibitors(thapsigargin, 2,5-di-(t-butyl)-1,4-benzohydroquinone)] inhibited the conjugation of p-nitrophenol. Depletion of intracellular Ca2+ stores by preincubation of hepatocytes in the absence of free Ca2+ (in the presence of excess EGTA) also decreased the rate of glucuronidation; Ca2+ re-admission to EGTA-treated hepatocytes restored glucuronidation. In intact liver microsomes the p-nitrophenol UDP-glucuronosyl-transferase activity was not modified by varying the external free Ca2+ concentrations within a cytosol-like range. Emptying of the Ca2+ from the lumen of microsomal vesicles by A23187, after MgATP-stimulated Ca2+ sequestration, decreased the glucuronidation of p-nitrophenol. A similar effect was observed in filipin-permeabilized hepatocytes. In native and in detergent-treated microsomes, Ca2+ (1-10 mM) increased the p-nitrophenol UDP-glucuronosyltransferase activity. It is suggested that the physiological concentration of Ca2+ in the lumen of the endoplasmic reticulum is necessary for the optimal activity of p-nitrophenol UDP-glucuronosyltransferase; the depletion of Ca2+ decreases the activity of the enzyme.

Bánhegyi, G., Bellomo, G., Fulceri, R., Mandl, J., & Benedetti, A. (1993). Intraluminal calcium of the liver endoplasmic reticulum stimulates the glucuronidation of p-nitrophenol. BIOCHEMICAL JOURNAL, 292(1), 99-104 [10.1042/bj2920099].

Intraluminal calcium of the liver endoplasmic reticulum stimulates the glucuronidation of p-nitrophenol

Fulceri, R.;Benedetti, A.
1993

Abstract

The relationship between the intraluminal Ca2+ content of endoplasmic reticulum and the rate of the glucuronidation of p-nitrophenol was investigated in isolated rat hepatocytes. Different agents which decrease the Ca2+ level in the endoplasmic reticulum [calcium ionophores (A23187, ionomycin) or Ca2+-ATPaseinhibitors(thapsigargin, 2,5-di-(t-butyl)-1,4-benzohydroquinone)] inhibited the conjugation of p-nitrophenol. Depletion of intracellular Ca2+ stores by preincubation of hepatocytes in the absence of free Ca2+ (in the presence of excess EGTA) also decreased the rate of glucuronidation; Ca2+ re-admission to EGTA-treated hepatocytes restored glucuronidation. In intact liver microsomes the p-nitrophenol UDP-glucuronosyl-transferase activity was not modified by varying the external free Ca2+ concentrations within a cytosol-like range. Emptying of the Ca2+ from the lumen of microsomal vesicles by A23187, after MgATP-stimulated Ca2+ sequestration, decreased the glucuronidation of p-nitrophenol. A similar effect was observed in filipin-permeabilized hepatocytes. In native and in detergent-treated microsomes, Ca2+ (1-10 mM) increased the p-nitrophenol UDP-glucuronosyltransferase activity. It is suggested that the physiological concentration of Ca2+ in the lumen of the endoplasmic reticulum is necessary for the optimal activity of p-nitrophenol UDP-glucuronosyltransferase; the depletion of Ca2+ decreases the activity of the enzyme.
Bánhegyi, G., Bellomo, G., Fulceri, R., Mandl, J., & Benedetti, A. (1993). Intraluminal calcium of the liver endoplasmic reticulum stimulates the glucuronidation of p-nitrophenol. BIOCHEMICAL JOURNAL, 292(1), 99-104 [10.1042/bj2920099].
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11365/28334
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