Catalytic Efficiency of a Photoenzyme—An Adaptation to Natural Light Conditions

Abstract

Cheap and safe: The catalytic efficiency of a light‐dependent photoenzyme (NADPH: protochlorophyllide oxidoreductase) is investigated as a function of the excitation wavelength (see picture). It becomes evident that “red” photons are more efficiently utilized in enzyme catalysis than “blue” photons. This shows an adaptation of the enzyme activity to the natural light conditions.

Stepwise Hydride Transfer in a Biological System: Insights into the Reaction Mechanism of the Light‐Dependent Protochlorophyllide Oxidoreductase

“…This model was applied onto the TA data resulting in reasonable SAS for each intermediate (Figure 3 D) with corresponding yields of Φ ( 2 I 0 (1) )=0.83, Φ ( 2 I 0 (2) )=0.5, Φ ( 1 I 0 (3) )=1.0, and Φ ( 1 C 0 )=1.0. Thus, the total quantum yield of 1 C 0 formation is Φ total ( 1 C 0 )= Φ ( 2 I 0 (1) ) Φ ( 2 I 0 (2) ) Φ ( 1 I 0 (3) ) Φ ( 1 C 0 )= Φ ( 2 I 0 (1) )=0.43, which is in good agreement with published data 28. However, we were not able to resolve the counter NADP(H) cation and neutral radicals, although they are expected to absorb in the same spectral regions ( λ max =370 and 550 nm and λ max =400 and 500 nm, respectively).…”

Plant Protochlorophyllide Oxidoreductases A and B

“…Both the turnover number k cat and the specificity constant k cat /K m commonly used for comparing enzyme activity are 2-and about 6-fold, respectively, larger for POR B than POR A. The 2-fold higher turnover number corresponds well with the previously reported 2-fold higher quantum efficiency of POR B versus POR A (21). One can speculate that the higher catalytic efficiency of POR B is related to its biological function.…”

Excited‐State Charge Separation in the Photochemical Mechanism of the Light‐Driven Enzyme Protochlorophyllide Oxidoreductase

“…However,i n contrast to free Pchlide and the Y193F variant there is an additional "reactive" pathway in wild-type POR from the S ICT state to yield SADS5 and SADS6 (the hydride transfer intermediate). Theq uantum yield of this pathway was set at 40 %inaccordance with previous estimates, [4,17,24] and is likely to reflect the orientation of the Pchlide molecule within the enzyme'sa ctive site.H ence,b ased on the time-resolved IR data we propose that there are 2r outes for the excited-state dynamics in wild-type POR-Pchlide-NADPH, which branch after formation of the S ICT state along "catalytic" and "noncatalytic" pathways.T his same model can then be applied to accurately fit the time-resolved visible data.…”