Abstract
Voltage- and current-clamp studies have been performed on a renal and intestinal protein (rBAT) which induces transport for neutral and dibasic amino acids when expressed in Xenopus oocytes. In current-clamp mode, superfusion with L-leucine caused a hyperpolarization while superfusion with L-arginine depolarized the oocyte. Accordingly, in voltage-clamp experiments dibasic amino acids and neutral amino acids induced inward and outward currents, respectively. The relationship between currents and substrate concentrations could be fitted by simple Michaelis-Menten kinetics. Currents induced by L-arginine and L-leucine were also voltage-dependent. pH changes from 6.25 to 8.75 did not affect the currents induced by saturating concentrations of L-arginine and L-leucine, but reversed the direction of L-histidine-induced currents from inward to outward. The reversal potentials as well as the apparent Km for L-histidine-induced currents were altered by the ambient pH. Currents induced by individual amino acids decreased during extended superfusion periods. However, extended superfusion with neutral amino acids increased dibasic amino acid induced currents, while prior superfusion with dibasic amino acid resulted in an increase of currents induced by neutral amino acids. The reversal potentials for L-leucine- and L-arginine-induced currents were depending on their intra- (after preloading) and extracellular concentrations. In conclusion, rBAT-mediated transport of neutral and dibasic amino acids is associated with net outward or inward currents, respectively, which may be caused by an exchange of neutral with dibasic amino acids.
Highlights
From the $National Institute for Basic Biology, Myodaiji, Okazaki 444, Japan, the §Department of Molecular Biomechanics, Graduate University of Advanced Studies, Myodaiji, Okazaki 444, Japan, /Biological Laboratory, Kyushu Uniuersity, Ropponmatsu, Fukuoka 810, Japan, and the **Department of Biology, College of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153, Japan
The biosynthesis of unsaturated form (Holloway, 19831, and the enzymes that catalyze the refatty acids is initiated by A9 acyl-lipid desaturase which action are knowans acyl-CoA desaturases andare bound tothe introduces the first double bondat the A9 position of a endoplasmic reticulum (Strittmatteret al., 1974)
Saturated fatty acid that has been esterified to a glyc- In the cyanobacterium Synechocystis sp
Summary
MOLECULAR CLONING AND SUBSTRATE SPECIFICITIES IN TERMS OF FATTY ACIDS, STZ-POSITIONSA, ND POLAR HEAD GROUPS*. We have cloned genes, designated de&, for A9 urated fatty acids are synthesizedvia sequential desaturation acyl-lipid desaturases from two cyanobacteria, namely of 18:O at the C-1 positionof glycerolipids to18:1(9), 18:1(9,12), AnabaenauariabilisandSynechocystissp. In addition to acyllipiddesaturases,higherplantscontain acyl-ACP’ desaturases, which introducea double bond only intosaturated fatty acids that are boundtoACP (McKeon and Stumpf,1982; Stumpf, 1981; Cahoon and Ohlrogge, 1994). PCC 6803 wasconstructed with a phage vector, ADASH I 1 (Stratagene, La Jolla, CA), as described previously (Sakamotoet al., 1994a).Approximately 2,500plaques of the
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