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Amino Acid Uptake by Pea Leaf Fragments

Specificity, Energy Sources, and Mechanism ¹

^a Department of Biology and Molecular Biology Institute, University of California, Los Angeles, California 90024

Amino acid uptake into leaf fragments of Pisum sativum depended on metabolism. Glycine uptake was optimal at 30 C and could be supported by respiration and by photosynthesis. Based on studies with an electron flow cofactor, inhibitors, and uncouplers, the energy source for glycine uptake was apparently ATP.

The energy-dependent transport of glycine was mediated by a carrier that had a broad specificity for neutral and positively charged L-amino acids. It readily translocated 15 such L-amino acids into the cells, but had a very low affinity for L-aspartate, L-glutamate, D-amino acids, and -aminoisobutyrate. The Ki for competitive inhibition of glycine uptake by another amino acid was equal to the Km for the uptake of that competing species.