UC Santa Cruz

This work examines the microsecond and millisecond photochemistry of human rhodopsin. There have been significant advances in the mechanistic and structural understanding of bovine rhodopsin over the last two decades that have not been applied to human rhodopsin. This study uses time-resolved absorbance spectroscopy to probe human rhodopsin in its native disk membrane. Human rhodopsin is first studied at pH 7.0 and 20°C from 1 µs - 128 µs to explore the lumirhodopsin I - lumirhodopsin II equilibrium. The remainder of this work examines human rhodopsin at pH 8.7 and 15°C from 5 µs - 120 ms to study the activation mechanism from lumirhodopsin I to metarhodopsin II. The intermediates seen in the bovine rhodopsin mechanism are present in human rhodopsin, but with differing kinetics. The processes observed in human rhodopsin are slower than in bovine rhodopsin, and the equilibria are shifted towards 380 nm product compared to bovine rhodopsin under similar conditions.