✦ LIBER ✦

A multicomponent analysis of amino acid transport systems in human lymphocytes. 1. Kinetic parameters of the A and L systems and pathways of uptake of naturally occurring amino acids in blood lymphocytes

✍ Scribed by George B. Segel; William Simon; Marshall A. Lichtman

Publisher: John Wiley and Sons
Year: 1983
Tongue: English
Weight: 708 KB
Volume: 116
Category: Article
ISSN: 0021-9541
DOI: 10.1002/jcp.1041160315

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✦ Synopsis

We have determined the kinetic parameters of natural and system-specific synthetic amino acid transport by human blood lymphocytes, using a multicomponent computer analysis that separates carrier-mediated uptake from diffusion. These studies were initiated in order to provide the basis for studies of human blood T and B lymphocytes and malignant lymphocytes. Methylaminoisobutyric acid (methyl-AIB) and 2-amino-2-carboxy-bicyclo (2,2,1) heptane (BCH) uptakes into lymphocytes were measured as prototypes of A-and L-system amino acid transport. The Michaelis constant for methyl-AIB uptake was 540 pM; the maximal velocity of uptake was 28 pnollL cell waterlmin, and t h e diffusion coefficient was .004 rnin-'. In contrast, the Michaelis constant for BCH uptake was 63 pM; the maximal velocity was 969 pmol/L cell water/ min, and the diffusion coefficient was .I41 m i d . The transport of the naturally occurring amino acids, alanine, proline, and leucine was defined by studies of: (1) competitive inhibition with t h e system-specific synthetic amino acids, methyl-AIB and BCH, ( 2 ) the effect of the transcellular sodium gradient on transport, and (3) evaluation of the time-dependent increase of transport in amino acid-deficient medium (adaptation). Alanine was transported principally (-70%) by the ASC-system, and leucine was transported principally (70%) by the L-system in lymphocytes. The analysis of proline transport was more complex because of a large component of uptake by diffusion even at low amino acid concentrations. Taken together, the kinetics of sodium-sensitive uptake and the results of competitive inhibition studies indicated that proline was transported by the A-system (30%), the ASC system (30%), and also by the L-system (15%).

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