Development of amino acid transport by the small intestine of the chick embryo

Abstract

1. 1. Amino acid transport by the small intestine of the chick was measured using the in vitro tissue-accumulation method. The developmental patterns for l-valine, glycine and l-lysine differ in a number of respects. Active transport of l-lysine was detected 4 days before hatching, that for l-valine 2 days before hatching, whereas active transport of glycine was first noted 1 day after hatching. The increase in active transport near hatching, seen with each amino acid tested, was most rapid with l-valine. 2. 2. The anaerobic glycolytic capacity of the small intestine decreased during the first week after hatching. The capacity for active transport under anaerobic conditions also decreased during this period. Immediately after hatching the rate of anaerobic transport of l-valine was 80% of the aerobic rate and 10 days later 5%. Although the rate of efflux and K m were essentially constant at those stages, the v max for l-valine uptake immediately after hatching was twice as great as at the later stage. 3. 3. The active transport of l-valine was shown to be Na +-dependent at the developmental stages examined. (Na + + K +)-ATPase (EC 3.6.1.3) was detected in subcellular fractions of the chick small intestine as early as 4 days before hatching. Prior to hatching its specific activity increased more rapidly in the mitochondrial than in the brush-border and microsomal membrane fractions.