The reinterpretation of the kinetics of the γ-glutamyl cycle-mediated uptake of amino acids in the light of the cycle's wave mechanical properties shows that its oscillatory periods are modulated by the chemical nature and the concentrations of amino acids. The periods of the cycle are the half-lives of glutathione whose function is to synchronize the oscillations of the two pathways of the cycle. γ-glutamyl transpeptidase, an amphipathic membrane protein and the master oscillator of the cycle degrades glutathione and translocates amino acids in a discontinuous manner suggesting that it flip-flops across the membrane, the periods of the flip-flops being the oscillatory periods of the γ-glutamyl transpeptidase/amino acid complexes. The energies of the flip-flops are quantized and independent of metabolic energy. The principal quantum numbers are dependent on the amino acids being translocated. In their translocation, those amino acids which are good substrates of the γ-glutamyl transpeptidase possess higher principal quantum numbers than those which are poor substrates, an observation which gives support to the flip-flopping of the γ-glutamyl transpeptidase/amino acid complexes across the cell membrane. © 1984 Academic Press Inc. (London) Ltd. All rights reserved.