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 a-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.

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