A silicon transporter is a membrane protein that moves a dissolved silicon-containing solute across a cell membrane. In the diatom SIT family, the substrate is silicic acid, the soluble precursor used in building a silica-rich cell wall. The functional category need not imply that transporters in every lineage have the same structure or coupling mechanism.[ref]
Direct evidence of the molecular basis for biological silicon transport by Michael J. Knight and others. Introduction and Discussion, diatom silicic-acid transport
A purified-system experiment reconstituted SIT proteins into liposomes. An inward-directed sodium gradient drove uptake, detected by fluorescence from zinc-dependent complexes formed inside the liposomes. Protein-free and unrelated-transporter controls helped distinguish transport from mixing background. Selected transporters had apparent Michaelis constants near .[ref]
Direct evidence of the molecular basis for biological silicon transport by Michael J. Knight and others. Figs.3–5, Zinc silicate fluorescence and Proteoliposome transport assays
Using that approximate scale in a simple Michaelis-Menten equation, gives at and at . This calculation illustrates saturation, not an additional experimental fit. A substrate-binding ratio measured at equilibrium does not by itself establish the number of sodium ions coupled to each transport event.
New to topics? Read the docs here!