Under certain conditions, some algae are able to produce hydrogen — a much sought-after green energy source. Its production takes place in the unique catalytic center of the unicellular algae and is only possible if certain cofactors of the relevant proteins are present. Researchers have identified how such a cofactor, the so-called hydrogen cluster, is assembled. Specifically, they describe the previously unexplained role of the enzyme HydF, which is involved in the final steps of assembly.