Hydrogen metabolism: A eukaryote taps into the electron sink

In vitro hydrogen production by mammal [FeFe]-hydrogenase-like protein

Although emerging evidence in mammals reveals that exogenously applied H2 positively regulates numerous physiological and pathological responses, it remains unclear whether and how mammalian cells produce H2 endogenously. Here, we report for the first time that recombinant human (Homo sapiens) and pig (Sus scrofa) nuclear prelamin recognition factor (Narf)-like proteins (also known as H. sapiens iron-only hydrogenase-like protein 1 [HsIOP1] and S. scrofa cytosolic iron-sulfur assembly component 3 [SsCIAO3], belonging to the [FeFe]-hydrogenase-like protein family), when expressed in a prokaryotic system, can potentially catalyze H2 production in vitro. Anaerobic induction was clearly observed. Further investigation of the transcriptome database revealed the widespread presence of these proteins in human and pig tissues. Sequence and structural analyses revealed that both HsIOP1 and SsCIAO3 may contain four conserved cysteine residues, forming a [4Fe4S] cluster, similar to the known [FeFe]-hydrogenase in Chlamydomonas reinhardtii. According to the observed hydrogenase activities of HsIOP1 and SsCIAO3 produced in Escherichia coli and the ubiquitous presence of Narf-like proteins in eukaryotic organisms, we propose that H2 production may be a universal phenomenon in eukaryotic organisms. Based on the results of the evolutionary tree, it was further hypothesized that hydrogen metabolism may have been ignored in the evolution and development of eukaryotic cells for a considerable time.

Phytomelatonin and gasotransmitters: a crucial combination for plant physiological functions

Melatonin, a molecule that was first identified in animal tissues, has been confirmed to be involved as a potential phytohormone in a variety of plant physiological responses. It is considered primarily as an antioxidant with important actions in controlling reactive oxygen and reactive nitrogen species. In addition to its role in regulating plant growth and development, phytomelatonin is involved in protection against abiotic and biotic stresses. The 'gasotransmitter'-that is, a gaseous signaling molecule-is a new concept that has been advanced in the past two decades, with functions in animal and plant physiological regulation. Gasotransmitters including nitric oxide, carbon monoxide, hydrogen sulfide, methane, and, more recently identified, hydrogen gas are critical and indispensable in a wide range of biological processes. This review investigates the interrelationship between phytomelatonin and the above-mentioned gasotransmitters from the perspective of biosynthetic origin and functions. Moreover, the potential future research directions for phytomelatonin and gasotransmitters interactions are discussed.