Multiphoton Manipulations of Enzymatic Photoactivity in Aspartate Aminotransferase

Photoinduced Reductive Dehalogenation of Phenacyl Bromides with Pyridoxal 5'-Phosphate

We describe the photoinduced reductive debromination of phenacyl bromides using pyridoxal 5'-phosphate (PLP). The reaction requires irradiation with cyan or blue light in an anaerobic atmosphere. Mechanistic analysis reveals the formation of the phenacyl radical as an intermediate in the reaction, implying a single electron transfer to phenacyl bromides from a PLP-derived species resulting from excitation by illumination.

The Effect of Visible Light on the Catalytic Activity of PLP-Dependent Enzymes

Pyridoxal 5'-phosphate (PLP)-dependent enzymes are a versatile class of biocatalysts and feature a variety of industrial applications. However, PLP is light sensitive and can cause inactivation of enzymes in certain light conditions. As most of the PLP-dependent enzymes are usually not handled in dark conditions, we evaluated the effect of visible light on the activity of PLP-dependent enzymes during production as well as transformation. We tested four amine transaminases, from Chromobacterium violaceum, Bacillus megaterium, Vibrio fluvialis and a variant from Arthrobacter species as well as two lysine decarboxylases, from Selenomonas ruminantium and the LDCc from Escherichia coli. It appeared that five of these six enzymes suffered from a significant decrease in activity by up to 90 % when handled in laboratory light conditions. Surprisingly, only the amine transaminase variant from Arthrobacter species appeared to be unaffected by light exposure and even showed an activation to 150 % relative activity over the course of 6 h regardless of the light conditions.

Photoenzymes and Related Topics: An Update

Photoenzymes are enzymes that catalyze photochemical reactions. For a long time, it was believed that only two types of photoenzymes exist: light-dependent NADPH:protochlorophyllide oxidoreductase and photolyase. However, other photoenzymes have now been discovered, most recently fatty acid photodecarboxylase.

Cycloreversion dynamics of a photochromic molecular switch via one-photon and sequential two-photon excitation

Ultrafast pump-probe (PP) and pump-repump-probe (PReP) measurements examine the ring-opening reaction of a photochromic molecular switch following excitation to the first and higher excited states. Sequential two-photon excitation is a sensitive probe of the excited-state dynamics, because the secondary excitation maps the progress along the S1 reaction coordinate onto the higher excited states of the molecule. In this contribution, secondary excitation at 800 nm accesses more reactive regions of the excited-state potential energy surfaces than are accessible with direct vertical excitation in the visible or UV. The quantum yield for cycloreversion increases by a factor of 3.5 ± 0.9 compared with one-photon excitation when the delay between the 500 nm pump and 800 nm repump laser pulses increases beyond ~100 fs, in contrast with a slower ~3 ps increase that was previously observed for one-color sequential excitation at 500 nm. The evolution of an excited-state absorption band reveals the dynamics of the higher-lying excited state for both one-photon excitation in the UV and sequential two-photon excitation. The spectroscopy and dynamics of the higher-lying excited state are similar for both excitation pathways, including a lifetime of ~100 fs. The complementary PP and PReP measurements provide a detailed picture of the ultrafast excited-state dynamics, including new insight on the role of excited states above S1 in controlling the photochemical cycloreversion reaction.