The photocycle of photoactive yellow protein

Scope and method of study. We studied the photocycle of Photoactive Yellow Protein (PYP).; Findings and conclusions. We performed exponential fitting with different numbers of exponentials on the flash photolysis data at 11 temperatures. By comparing the standard deviations with the numbers of exponentials used, we concluded that 4 exponentials are most appropriate to fit the flash photolysis data. Therefore, the PYP photocycle is best described with 4 intermediates according to the first-order kinetics theorem. In additional to p R, pB' and pB, there is an intermediate state PYPN formed during the recovery of pG from pB. Additional studies are needed to characterize this intermediate. The global analysis of the flash photolysis data prompted a further experimental investigation of the temperature dependence of the pG absorption in the UV/vis region. We demonstrated that the pG absorption is strongly temperature dependent. This impedes the multi-temperature global modeling of the flash photolysis data. We also found that as temperature increases, pB dark is formed. By analyzing the FTIR stepscan data, the bi-exponential properties of the 1726 cm-1 and 1514--1498 cm -1 bands proved the existence of the back reaction from pB' to pR. With population model fitting, we obtained the actual rate constants for the PYP intermediates transitions at 300 K for our new photocycle model. Our new photocycle model contains an additional intermediate PYPN and one back reaction from pB' to pR. (Abstract shortened by UMI.)...