4a. It is also commonly used as a more general
phenomenological equation to fit data and has been directly applied to quantify the relationship between lumen pH and qE, as in Fig. 4b. The Hill equation has the form $$ F = \frac[H^+]^n [H^+]^n +[10^-p\it K_a]^n, $$ (3)where F is the fraction of proteins that are activated. The Hill equation contains two parameters: the pK a, which is the pH at which F = 0.5, and the Hill coefficient n, which is MM-102 a measure of the sigmoidicity, or “steepness,” of the transition of F from a “100 % on” state to a “100 % off” state. In the case when a protein must bind multiple protons to be activated, and when this binding is highly cooperative, the Hill coefficient n can be interpreted as the number of protons needed to activate the protein, as in the reaction $$ A + n H^+ \rightleftharpoons A H^+_n. $$ (4) In the case when binding is not extremely cooperative, the Hill coefficient still measures the cooperativity of binding, but does not correspond directly
to a physical property such as the number of protonatable sites (Weiss 1997). The existing measurements from several labs fit quite well to the Hill equation. However, the Hill equation does not directly correspond to a physical model in most situations (Weiss 1997). As a {Selleck Anti-cancer Compound Library|Selleck Anticancer Compound Library|Selleck Anti-cancer Compound Library|Selleck Anticancer Compound Library|Selleckchem Anti-cancer Compound Library|Selleckchem Anticancer Compound Library|Selleckchem Anti-cancer Compound Library|Selleckchem Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|Anti-cancer Compound Library|Anticancer Compound Library|buy Anti-cancer Compound Library|Anti-cancer Compound Library ic50|Anti-cancer Compound Library price|Anti-cancer Compound Library cost|Anti-cancer Compound Library solubility dmso|Anti-cancer Compound Library purchase|Anti-cancer Compound Library manufacturer|Anti-cancer Compound Library research buy|Anti-cancer Compound Library order|Anti-cancer Compound Library mouse|Anti-cancer Compound Library chemical structure|Anti-cancer Compound Library mw|Anti-cancer Compound Library molecular weight|Anti-cancer Compound Library datasheet|Anti-cancer Compound Library supplier|Anti-cancer Compound Library in vitro|Anti-cancer Compound Library cell line|Anti-cancer Compound Library concentration|Anti-cancer Compound Library nmr|Anti-cancer Compound Library in vivo|Anti-cancer Compound Library clinical trial|Anti-cancer Compound Library cell assay|Anti-cancer Compound Library screening|Anti-cancer Compound Library high throughput|buy Anticancer Compound Library|Anticancer Compound Library ic50|Anticancer Compound Library price|Anticancer Compound Library cost|Anticancer Compound Library solubility dmso|Anticancer Compound Library purchase|Anticancer Compound Library manufacturer|Anticancer Compound Library research buy|Anticancer Compound Library order|Anticancer Compound Library chemical structure|Anticancer Compound Library datasheet|Anticancer Compound Library supplier|Anticancer Compound Library in vitro|Anticancer Compound Library cell line|Anticancer Compound Library concentration|Anticancer Compound Library clinical trial|Anticancer Compound Library cell assay|Anticancer Compound Library screening|Anticancer Compound Library high throughput|Anti-cancer Compound high throughput screening| result, extracting mechanistic information from measurements of qE measured as a function of lumen pH is challenging. One way forward is through the development of physically motivated mathematical models that explicitly incorporate each protonation event in various hypotheses of qE mechanism. In the following sections, we review measurements correlating lumen pH and the hypotheses that have been generated from these measurements. Measurements of qE triggering ΔpH or low lumen pH? For understanding the processes triggering qE, it is important to differentiate between those processes that only require a low lumen pH and processes that require a \(\Updelta\hboxpH\) across the thylakoid membrane. The protonation of residues in PsbS, VDE, and LHC proteins can be accomplished by lowering
the lumen pH, without necessarily requiring a pH gradient Racecadotril across the thylakoid membrane. However, work by Goss et al. (2008) demonstrated that a pH gradient across the thylakoid membrane, along with a neutral or slightly basic stromal pH, is required for the formation of zeaxanthin-dependent qE. Once qE is formed, it is possible to maintain qE even in the absence of a pH gradient if the lumen pH is kept sufficiently low (Rees et al. 1992). This property was used to determine the qE versus pH curves in Johnson and Ruban (2011) and Johnson et al. (2012). The ability to maintain qE in low pH, even without a \(\Updelta\hboxpH,\) see more suggests that the \(\Updelta\hboxpH\) is required for proper insertion of zeaxanthin (Goss et al. 2008), but that other pH-sensitive components of qE do not require a pH gradient.