Cryptochrome*

Cryptochrome is a blue-light photoreceptor protein involved in both plant and animal circadian rhythms. When illuminated by blue light, the flavin cofactor of cryptochrome is photoreduced, thus yielding the active state of the protein. This photoreduction and subsequent reoxidation can be observed spectroscopically. However, the effect of temperature on the photoreduction has not been extensively studied. Here, using a UV-Vis spectrophotometer, we demonstrate the effects of temperature on the photoreduction and reoxidation of purified Arabidopsis cryptochrome 1 (AtCry1) and cryptochrome 2 (AtCry2) proteins. It was hypothesized that at higher temperature, an increase in the rate of photoreduction and reoxidation would occur. However, our experimental results demonstrated that when comparing the reactions at 15°C and 25°C, temperature had no effect on the photoreduction of the flavin, but the rate of reoxidation was increased at the higher temperature. These results suggest increased activation in AtCry1 and AtCry2 at lower temperatures.