Christensen H N, Handlogten M E
Proc Natl Acad Sci U S A. 1975 Jan;72(1):23-7. doi: 10.1073/pnas.72.1.23.
Although lowering the pK2 of neutral amino acids only weakens their concentrative uptake by Ehrlich cells, the same change greatly enhances uptake of diamino acids. This effect does not arise merely from putting the distal amino group in its uncharged form, but depends on an enhanced deprotonation of the alpha-amino group. Parallel effects are seen for the transport system for basic amino acids, for which the assignment of pK values within the membrane is less ambiguous. To explain the paradoxical advantages of having the alpha-amino group protonated yet readily deprotonated, we propose that a proton withdrawn from that group is pumped over an intramembrane interval to energize amino-acid transport.
虽然降低中性氨基酸的pK2仅会削弱艾氏细胞对它们的浓缩摄取，但同样的变化会大大增强二氨基酸的摄取。这种效应并非仅仅源于使远端氨基处于不带电荷的形式，而是取决于α-氨基去质子化的增强。对于碱性氨基酸的转运系统也观察到了类似的效应，其在膜内的pK值分配不太模糊。为了解释α-氨基质子化但又易于去质子化所具有的矛盾优势，我们提出从该基团抽出的一个质子被泵过膜内间隔以驱动氨基酸转运。
