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The channel has a large diameter of 0.8x1.1nm, and is non-selective for small ions. However, it has an upper exclusion size limit corresponding to molecular weights of about 600 Dalton of permeants. Because most metabolites have molecular weights lower than 600 Da and have been shown to pass through porin channels, porins are called general diffusion pores.
The lower most region of the ionosphere extending from about 50 km to 90 km is the D-region, which principally absorbs radio waves. Above the D layer is the E-region extending from 90 km to 150 km.