微生物吸收营养物质的方式1单纯扩散.PPT

Ion driven transport systems (IDT) and Binding-protein dependent transport systems (BPDT) are active transport systems that are used for transport of most solutes by bacterial cells. IDT is used for accumulation of many ions and amino acids; BPDT is frequently used for sugars and amino acids. IDT is a symport or antiport process that uses a hydrogen ion (H+) i.e., proton motive force (pmf), or some other cation, i.e.,chemiosmotic potential, to drive the transport process. IDT systems such as the lactose permease of E. coli utilize the consumption of a hydrogen ion during the transport of lactose. Thus the energy expended during active transport of lactose is in the form of pmf. The lactose permease is a single transmembranous polypeptide that spans the membrane seven times forming a channel that specifically admits lactose. Binding-protein dependent transport systems, such as the histadine transport system in E. coli, are composed of four proteins. Two proteins form a membrane channel that allows passage of the histadine. A third protein resides in the periplasmic space where it is able to bind the amino acid and pass it to a forth protein which admits the amino acid into the membrane channel. Driving the solute through the channel involves the expenditure of energy, which is provided by the hydrolysis of ATP. Group translocation systems (GT), more commonly known as the phosphotransferase system (PTS) in E. coli, are used primarily for the transport of sugars. Like binding protein-dependent transport systems, they are composed of several distinct components. However, GT systems specific for one sugar may share some of their components with other group transport systems. In E. coli, glucose may be transported by a group translocation process that involves the phosphotransferase system. The actual carrier in the membrane is a protein channel fairly specific for glucose. Glucose specifically enters the channel from the outside, but in order to exit into the cytoplasm