Rost S, Frank C, Beck E
Lehrstuhl f. Pflanzenphysiologie, Universität Bayreuth, Germany.
Biochim Biophys Acta. 1996 Dec 6;1291(3):221-7. doi: 10.1016/s0304-4165(96)00068-2.
Permeation of [14 C]maltose into the stroma (measured as the sorbitol-impermeable space) of isolated intact spinach (Spinacia oleracea L.) chloroplasts was studied using the silicone oil centrifugation technique. Maltose uptake showed Michaelis Menten-kinetics with a K(m) of 25 mM and a Vmax of 19.5 mumol maltose. mg Chl-1. h-1 at 15 degrees C. Lack of interaction of glucose and maltose uptake suggested the presence of individual translocators for maltose and glucose in the inner chloroplast envelope. Maltose uptake was markedly inhibited by maltodextrins (maltotriose up to maltoheptaose). The corresponding [14C]maltodextrins were prepared by degradation of [14C]starch with pullulanase and alpha-amylase and purified by high performance TLC. None of these maltodextrins, when administered at a concentration of 10 mM, was transported into the sorbitol-impermeable space of the chloroplasts. The results suggest that the transport system for maltose is also accessible to maltodextrins but that only maltose can be translocated across the inner envelope of spinach chloroplasts.
采用硅油离心技术研究了[¹⁴C]麦芽糖进入离体完整菠菜（Spinacia oleracea L.）叶绿体基质（以山梨醇不可渗透空间衡量）的渗透情况。麦芽糖摄取呈现米氏动力学，在15℃时，米氏常数（K(m)）为25 mM，最大反应速度（Vmax）为19.5 μmol麦芽糖·mg叶绿素⁻¹·h⁻¹。葡萄糖和麦芽糖摄取之间缺乏相互作用，表明叶绿体内膜中存在麦芽糖和葡萄糖各自的转运体。麦芽糖摄取受到麦芽糊精（麦芽三糖至麦芽七糖）的显著抑制。相应的[¹⁴C]麦芽糊精通过用支链淀粉酶和α-淀粉酶降解[¹⁴C]淀粉制备，并通过高效薄层层析纯化。当以10 mM的浓度施用时，这些麦芽糊精均未转运到叶绿体的山梨醇不可渗透空间中。结果表明，麦芽糖转运系统对麦芽糊精也有作用，但只有麦芽糖能够跨菠菜叶绿体的内膜进行转运。
