. Biological transport. Biological transport; Biological Transport. BIOLOGICAL TRANSPORT site by an apolar bond. The direction of this bond is probably not especially critical, since hydrocarbon groups of various lengths and branchings can serve. Perhaps the small but definite affinity shown by the d isomers (about one-tenth that shown by their l enantio- morphs) arises from a degree of flexibility in the direction of this third point of attachment. Conceivably, the large hydrocarbon groups, rather than serving statically as a third point of attach- ment, could facilitate the passage or creepi
. Biological transport. Biological transport; Biological Transport. BIOLOGICAL TRANSPORT site by an apolar bond. The direction of this bond is probably not especially critical, since hydrocarbon groups of various lengths and branchings can serve. Perhaps the small but definite affinity shown by the d isomers (about one-tenth that shown by their l enantio- morphs) arises from a degree of flexibility in the direction of this third point of attachment. Conceivably, the large hydrocarbon groups, rather than serving statically as a third point of attach- ment, could facilitate the passage or creeping of the solute mole- cules from one polar site to another, by bonding transiently to corresponding hydrocarbon sites in the membrane. As Figure 20 shows, however, the whole story of the uptake of neutral amino acids by the Ehrlich cell is more complex than the two preceding paragraphs may have suggested. The curve marked Leucine shows how quickly the amino acids with large hydrocarbon 20. 20 40 60 Time, min Figure 20 Time course of the uptake of four amino acids by the Ehrlich ascites tumor cell. The curve for a-aminoisobutyric acid uptake resembles that for glycine except that higher distribution ratios are reached. "Cycloleucine" designates 1-aminocyclopentanecarboxylic acid. [From Christ ens en et al. (1962), in J. F. Holto?i (ed.), Conference on Free Amino Acids, Elsevier, Amsterdam; with permission.] 56. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Christensen, Halvor N. New York, W. A. Benjamin
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