Enzyme AsLOX2 Identified as First Step in Making Saclipin, a UV-Absorbing Compound From an Edible Cyanobacterium

Researchers at Meijo University in Japan found the enzyme that handles the starting step in the biosynthesis of saclipins A and B, UV-absorbing compounds made by Aphanothece sacrum (Japanese name suizenji-nori), an edible freshwater cyanobacterium. The key finding is that the fatty acid oxidizing enzyme lipoxygenase AsLOX2 attaches oxygen to carbons 9 and 16 of alpha-linolenic acid (α-linolenic acid) to make a hydroperoxide intermediate. The paper was published in the Journal of Natural Products and reported by Phys.org.

One enzyme found, the rest filled in with chemistry

The team selected two lipoxygenase candidates (AsLOX1 and AsLOX2) from the cyanobacterial genome, made them as recombinant proteins and compared their activity. AsLOX2 showed the highest activity on alpha-linolenic acid and converted more than 80% of the substrate to the intermediate within minutes under optimal conditions. AsLOX1, by contrast, showed no detectable activity under the test conditions. Because the enzyme that converts the intermediate into saclipin has not yet been found, the team used chemical reactions, reduction with tin chloride (SnCl2) and oxidation with manganese dioxide (MnO2), to convert the intermediate into saclipins A and B (about 9 to 1) and confirmed that they matched the natural compounds.

Saclipin strongly absorbs ultraviolet light around 316 to 319 nm and has been mentioned as a candidate for a naturally derived UV-blocking material. By revealing the entrance to the biosynthetic pathway, this study is significant in offering an experimental route to obtain saclipin without relying only on microbial culture.

However, the enzymes in the later part of the pathway remain unidentified, and the yield of the chemical conversion steps was reported only as "not high." Productivity, safety and stability have not been evaluated, so applications such as cosmetics are still a long way off.