General Properties of 14C-L-Valine-Binding to Human Brain Tissue
L-Valine (VAL) binding is saturable, reversible, linear within a protein concentration of 0.2 to 0.8 mg prot./ml, pH dependent (pH-optimum 7.1 to 7.4), temperature dependent with extremely low binding at 0–4° C; the assay runs at 37 °C; it is ion dependent (Bmax: CaCl2 (5 mM): + 100%; NaCl (5 mM): −50%; very sensitive to TRITON X-100 (Bmax at 0.01%: − 70%); N-ethylmaleimide (0.5 mM): Competitive inhibition; no change in nonspecific binding; there are no effects by puromycine plus GTP; VAL binds to synaptic membranes of human frontal cortex with KD-values several fold lower than that observed with homogenates, the distribution of VAL-binding is different in various human brain areas and can be inhibited by L-leucine, L-isoleucine, L-serine, DL-threonine, glycine and D-valine, while aromatic amino acids, β-alanine, GABA, taurine, glutamate, proline and γ-glutamyltaurine have no effects at 10−3 M.
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