Transport of neutral amino acids by adult articular cartilage.
The transport of three neutral amino acids: alanine, serine and leucine and the non-metabolizable analogue aminoisobutyric acid (AIB) was characterized in bovine articular cartilage slices. Alanine and serine were strongly concentrated intracellularly by a factor of 4.5 and 5 respectively and were transported in a sodium dependent and pH sensitive manner. AIB was concentrated by a factor of 1.8 with respect to the extracellular medium and was also transported in a sodium dependent and pH sensitive manner. Leucine was concentrated weakly across the chondrocyte membrane (X1.1) and its transport was independent of sodium ion concentration and the lowering of the extracellular pH. The apparent Km of transport of alanine, serine, leucine and AIB was determined to be 0.46 mM, 0.69 mM, 0.93 mM and 0.66 mM respectively and the values of Vmax were 35.8, 52.1, 14.8 and 6.8 pmol/min per mg respectively. It was shown that both alanine and serine were transported predominantly by system ASC (63.8% and 67.4% respectively) with a small percentage of transport occurring via system A. AIB was transported mainly by system A (76.0%) and leucine was transported equally via systems L (48.4%) and ASC (45.0%).
D000409:Alanine / Q000378:metabolism*; D000596:Amino Acids / Q000494:pharmacology; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D002358:Cartilage, Articular / Q000378:metabolism*; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008297:Male; D012694:Serine / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013379:Substrate Specificity
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D012694:Serine; D012964:Sodium; D007930:Leucine; D000409:Alanine