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.
We have determined the kinetic parameters of natural and system-specific synthetic amino acid transport by human blood lymphocytes, using a multi-component 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 microM; the maximal velocity of uptake was 28 mumol/L cell water/min, and the diffusion coefficient was .004 min-1. In contrast, the Michaelis constant for BCH uptake was 63 microM; the maximal velocity was 969 mumol/L cell water/min, and the diffusion coefficient was .141 min-1. The transport of the naturally occurring amino acids, alanine, proline, and leucine was defined by studies of: (1) competitive inhibition with the 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 (approximately 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%).
D000596:Amino Acids / Q000097:blood*; D001402:B-Lymphocytes / Q000378:metabolism; D001667:Binding, Competitive; D001692:Biological Transport; D002478:Cells, Cultured; D004058:Diffusion; D006801:Humans; D007700:Kinetics; D007938:Leukemia / Q000097:blood; D008214:Lymphocytes / Q000378:metabolism*; D012964:Sodium / Q000097:blood; D013601:T-Lymphocytes / Q000378:metabolism
D000596:Amino Acids; D012964:Sodium