In isolated brain microvessels, used as an in vitro model of the blood-brain barrier, the rate of hypoxanthine uptake was modulated by the presence of inorganic phosphate. A single high-capacity, low-affinity transport system was apparently active in a phosphate-free medium (Vmax = 840 pmol/mg protein/min, Km = 750/uM); in the presence of 10 mM phosphate, there was also a low-capacity, high-affinity system (Vmax = 47 pmol/mg protein/min, Km = 27/uM). The phosphate-dependent component was inactive in the absence of glucose or of Na+ ions, or upon addition of phloretine (but was scarcely affected by 2,4-dinitrophenol). This activity was apparently coupled to the intracellular phosphoribosyltransferase-catalyzed conversion of purines into the corresponding nucleotides: when inorganic phosphate was present in the suspending medium, labeled hypoxanthine was transported with higher efficiency and was readily converted to inosine monophosphate and to other related nucleotides. In the absence of phosphate ions, hypoxanthine was instead metabolized to xanthine and uric acid.
Effect of inorganic phosphate on hypoxanthine transport in isolated brain microvessels / Cardelli, Patrizia; Fiori, Anna; Santulli, Maria; Ceci, Fabrizio; Salerno, Costantino; Savi, Maria Rosaria; Peresempio, V.; Strom, Roberto. - In: BIOCHEMISTRY INTERNATIONAL. - ISSN 0158-5231. - STAMPA. - 28:5(1992), pp. 823-834.
Effect of inorganic phosphate on hypoxanthine transport in isolated brain microvessels
CARDELLI, Patrizia;FIORI, Anna;SANTULLI, Maria;CECI, Fabrizio;SALERNO, Costantino;SAVI, Maria Rosaria;STROM, Roberto
1992
Abstract
In isolated brain microvessels, used as an in vitro model of the blood-brain barrier, the rate of hypoxanthine uptake was modulated by the presence of inorganic phosphate. A single high-capacity, low-affinity transport system was apparently active in a phosphate-free medium (Vmax = 840 pmol/mg protein/min, Km = 750/uM); in the presence of 10 mM phosphate, there was also a low-capacity, high-affinity system (Vmax = 47 pmol/mg protein/min, Km = 27/uM). The phosphate-dependent component was inactive in the absence of glucose or of Na+ ions, or upon addition of phloretine (but was scarcely affected by 2,4-dinitrophenol). This activity was apparently coupled to the intracellular phosphoribosyltransferase-catalyzed conversion of purines into the corresponding nucleotides: when inorganic phosphate was present in the suspending medium, labeled hypoxanthine was transported with higher efficiency and was readily converted to inosine monophosphate and to other related nucleotides. In the absence of phosphate ions, hypoxanthine was instead metabolized to xanthine and uric acid.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.