difference between protein channels and protein carriers
Cavity in a carrier protein is not open simultaneously to the both environment (extracellular and intracellular). Either its inner gate is open, or outer gate is open, Carrier has binding sites, but porins and channel proteins have not. When a channel is opened, thousands to millions of ions can pass through the membrane in one time, but only one or a small amount of molecules can pass through a carrier molecule.
The transmembrane electron transfer carriers in the membrane include two-electron carriers, such as the disulfide bond oxidoreductases (DsbB and DsbD in E. coli) as well as one-electron carriers such as NADPH oxidase. Often these redox proteins are not considered transport proteins.