Hamaide F, Sprott GD, Kushner DJ. Energetics of sodium-dependent alpha-aminoisobutyric acid transport in the moderate halophile Vibrio costicola.
BIOCHIMICA ET BIOPHYSICA ACTA 1984;
766:77-87. [PMID:
6743651 DOI:
10.1016/0005-2728(84)90219-6]
[Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The energetics of alpha-aminoisobutyric acid transport were examined in Vibrio costicola grown in a medium containing the NaCl content (1 M) optimal for growth. Respiration rate, the membrane potential (delta psi) and alpha-aminoisobutyric acid transport had similar pH profiles, with optima at 8.5-9.0. Cells specifically required Na+ ions to transport alpha-aminoisobutyric acid and to maintain the highest delta psi (150-160 mV). Sodium was not required to sustain high rates of O2-uptake. Delta psi (and alpha-aminoisobutyric acid transport) recovered fully upon addition of Na+ to Na+-deficient cells, showing that Na+ is required in formation or maintenance of the transmembrane gradients of ions. Inhibitions by protonophores, monensin, nigericin and respiratory inhibitors revealed a close correlation between the magnitudes of delta psi and alpha-aminoisobutyric acid transport. Also, dissipation of delta psi with triphenylmethylphosphonium cation abolished alpha-aminoisobutyric acid transport without affecting respiration greatly. On the other hand, alcohols which stimulated respiration showed corresponding increases in alpha-aminoisobutyric acid transport, without affecting delta psi. Similarly, N,N'-dicyclohexylcarbodiimide (10 microM) stimulated respiration and alpha-aminoisobutyric acid transport and did ot affect delta psi, but caused a dramatic decline in intracellular ATP content. From these, and results obtained with artificially established energy sources (delta psi and Na+ chemical potential), we conclude that delta psi is obligatory for alpha-aminoisobutyric acid transport, and that for maximum rates of transport an Na+ gradient is also required.
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