Active Ca2+ transport by membrane vesicles from pigeon erythrocytes Stimulation by amino acids,ATP, GTP,P1 and some other cell constituents |
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Authors: | Jean W Lee George A Vidaver |
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Institution: | Department of Chemistry, University of Nebraska, Lincoln, NE 68588 U.S.A. |
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Abstract: | Pretreatment of pigeon erythrocyte membrane vesicles with amino acids, ATP, GTP, Pi and some other simple cell constituents (singly and in combination) causes an increase in ATP-dependent Ca2+-uptake activity of vesicles upon subsequent incubation with 45Ca2+ after removal of the above agents from the ‘i’ face. Amino acids augment the stimulation by all stimulatory agents and are required for stimulation by Pi. The effects of amino acids, ATP, GTP and Pi all occur at physiological concentrations. Many if not all of the effects of the mixture of amino acids that occur naturally in the cells can be accounted for by the group transported by the ‘ASC’ transport system of Christensen (Christensen H.N. (1975) Biological Transport, 2nd edn., W.A. Benjamin, Inc., Reading, MA), but not by any single amino acid at its physiological concentration. The effects of ATP and GTP are not mimicked by their non-hydrolysable β, γ-imido analogues nor by the corresponding 3′, 5′-cyclic monophosphates. None of the effects described appears to involve calmodulin. We suggest that amino acid transport plays a role in metabolic regulation through effects on cell Ca2+]. Analogous effects on cell Ca2+] may be involved in the action of the many hormones which augment amino acid accumulation by the ‘A’ amino acid transport system. |
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Keywords: | Amino acid stimulation Nucleotide stimulatio (Pigeon erythrocyte membrane) EGTA Tes GMPPNP guanosine 5′ -[β γ-imido]triphosphate tetrasodium salt AMPPNP adenosine 5′ -[β γ-imido]triphosphate NNP |
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