Abstract: Archaerorhodopsin-4（aR4） is a photoreceptor containing carotenoid chromophore from Halobacte-rium species XZ515. It has a similar trimeric structure and a light-driven proton pump function as bacteriorhodopsin（bR）. Although both aR4 and bR are outward proton pumps, aR4 exhibits a reversed temporal order of proton release and uptake compared with bR. Arginine 82, located in the extracellular half channel of bR, bridges the connection between the retinal binding pocket and proton release cluster（PRC）. It propagates the protonation status of D85 to the extracellular side and regulates proton release and reprotonation of PRC. R83 is the corresponding residue in aR4 but has a different orientation for its sidechain compared with R82 in bR. So far, nothing is clear about this orientation difference with the temporal order of proton release. This paper uses site-specific mutagenesis, combined with in situ UV-Vis absorption spectroscopy, flash light-induced transient absorption change measurements, and acid-base titration to explore the function difference of R83 in aR4 and R82 in bR. The results show that both R83 and R82 act as a "bridge" to link the proton acceptor and PRC in two proteins, but the hydrogen bond interaction of R83 with PRC is weaker than R82 with PRC in bR, which might be one of the reasons for the different temporal order of proton release in aR4. In addition, removing bacterioruberin in aR4 will increase the pH dependence of the R83 function.