Molecular hydrogen (H2) is an important molecule in the metabolism of diverse microorganisms. It is used either as energy source or for the disposal of reducing equivalents depending on environmental conditions. Furthermore, H2 transmits energy between different species within microbial communities. The enzymes that split or evolve H2 are called hydrogenases and these metalloproteins can be divided into three phylogenetically unrelated classes distinguishable by the metal composition of their active sites, namely [Fe]-, [FeFe]-, and [NiFe]- hydrogenases. Following a century of hydrogenase research, it is now possible to isolate, handle, and investigate these fragile enzymes. There have been numerous advances in understanding the regulation, function, structures, and maturation of these enzymes, as well as their involvement in important processes such as microbial pathogenesis and biogeochemical cycling. The employment of hydrogenases and hydrogenase-based applications could also potentially facilitate the world’s transition to a future sustainable H2-based energy economy.

Metals are present in nearly half of all enzymes, often at the active site, where they modulate catalytic function. Some of these metalloenzymes exist with a single bound metal ion while many others contain complex metal clusters. Complex FeS assemblies are associated with the interconversion of the small molecules H 2, CO, CO 2, N 2, and NH 3. One such complex metalloenzyme, [FeFe]-hydrogenase, catalyzes the reversible oxidation of molecular H 2. The active site of [FeFe]-hydrogenases, the Hcluster, exists as a [4Fe-4S]-subcluster bridged by a protein thiolate ligand to a 2Fesubcluster which contains biologically unique CO and CN- ligands and a dithiolate ligand. The H-cluster is synthesized by the activities of the hydrogenase maturation enzymes HydE, HydF, and HydG and until recently little was known concerning the biosynthetic pathway for the H-cluster. The results presented here provide significant insight into the stepwise mechanism of H-cluster biosynthesis. Biochemical and spectroscopic characterization of the structural [FeFe]-hydrogenase enzyme expressed in a genetic background devoid of maturation genes hydE, hydF, and hydG (HydA Delta EFG) indicates by the presence of a [4Fe-4S] cluster required for [FeFe]-hydrogenase activation that the [4Fe-4S]-subcluster and 2Fe-subcluster of the H-cluster are synthesized independently. The determination of the x-ray crystal structure of HydA Delta EFG confirms this by revealing the presence of the [4Fe-4S]-subcluster and an open binding pocket for the 2Fe-subcluster, indicating that H-cluster synthesis is directed in a stepwise manner with synthesis and insertion of the [4Fe-4S]-subcluster occurring first by generalized host cell machinery followed by synthesis and insertion of the 2Fe-subcluster by specialized hyd encoded maturation machinery. The structure also reveals that insertion of the 2Fe-subcluster occurs through a positively charged channel that collapses following incorporation, as a result of conformational changes in two conserved loop regions. By utilizing complementary gene data base searching with these structural studies, new insight is made known into the evolutionarily relationships between [FeFe]-hydrogenases present in microorganisms and the eukaryotic Nar1 family of proteins which function in iron-sulfur cluster biosynthesis. The work presented as a whole, by establishing parallels to complex metal cofactor biosynthesis in nitrogenase, reveals unifying themes in complex metal cluster assembly and fundamental features of metalloenzyme evolution.

There continues to be widespread interest in the applications of hydrogen as a clean fuel and its potential for local electricity production and use in transport. Recent years have seen a variety of breakthroughs in our understanding of the nature, structure, and biosynthesis of hydrogenases. This book is a timely description of these developments,

The Enzymes, Volume 54 highlights new advances in enzymes, with new chapters on a variety of topics, including the History of The Enzymes, Impact of The Enzymes in chronicling biochemical processes and pathways, Metabolism and Catalysis, Mitochondrial ATP synthase, The respiratory chain, A century of mitochondrial research, Five decades of metalloenzymology, Mechanisms of catalysis, Mitochondrial fatty acid synthesis and associated processes, Signaling, MAPK cascades: Origins, mechanisms and current status, Sphingolipids: From structural components to signaling hubs, Protein Homeostasis and Hydrolysis, Mitochondrial AAA+ proteases, Hsp70 and JDP proteins: structure-function perspective on molecular chaperone activity. Other sections cover DNA Replication and Repair, Structure-function studies of DNA replication proteins, and Helicases required for nucleotide excision repair. Provides the authority and expertise of leading contributors from an international board of authors Updated release includes the latest information on enzymes

The central theme of this book “Microbial BioEnergy: Hydrogen Production” is focused on the biological machinery that microorganisms use to produce hydrogen gas. The book summarizes the achievements over the past decade in the biochemistry, structural and molecular biology, genomics and applied aspects of microbial H2-production, including microbial fuel cells (MFC), by phototrophs such as purple sulfur and non-sulfur bacteria (Thiocapsa spp., Rhodobacter and Rhodopseudomonas spp.) microalgae (Chlamydomonas) and cyanobacteria (Anabaena spp.) along with anaerobes and thermophiles such as Caldicellulosiruptor and Thermotoga. This is the first book of this series entirely devoted to microbial bio-hydrogen production and is intended to be a precious source of information for PhD students, researchers and undergraduates from disciplines such as microbiology, biochemistry, biotechnology, photochemistry and chemical engineering, interested in basic and applied sciences.

The Prokaryotes is a comprehensive, multi-authored, peer reviewed reference work on Bacteria and Achaea. This fourth edition of The Prokaryotes is organized to cover all taxonomic diversity, using the family level to delineate chapters. Different from other resources, this new Springer product includes not only taxonomy, but also prokaryotic biology and technology of taxa in a broad context. Technological aspects highlight the usefulness of prokaryotes in processes and products, including biocontrol agents and as genetics tools. The content of the expanded fourth edition is divided into two parts: Part 1 contains review chapters dealing with the most important general concepts in molecular, applied and general prokaryote biology; Part 2 describes the known properties of specific taxonomic groups. Two completely new sections have been added to Part 1: bacterial communities and human bacteriology. The bacterial communities section reflects the growing realization that studies on pure cultures of bacteria have led to an incomplete picture of the microbial world for two fundamental reasons: the vast majority of bacteria in soil, water and associated with biological tissues are currently not culturable, and that an understanding of microbial ecology requires knowledge on how different bacterial species interact with each other in their natural environment. The new section on human microbiology deals with bacteria associated with healthy humans and bacterial pathogenesis. Each of the major human diseases caused by bacteria is reviewed, from identifying the pathogens by classical clinical and non-culturing techniques to the biochemical mechanisms of the disease process. The 4th edition of The Prokaryotes is the most complete resource on the biology of prokaryotes. The following volumes are published consecutively within the 4th Edition: Prokaryotic Biology and Symbiotic Associations Prokaryotic Communities and Ecophysiology Prokaryotic Physiology and Biochemistry Applied Bacteriology and Biotechnology Human Microbiology Actinobacteria Firmicutes Alphaproteobacteria and Betaproteobacteria Gammaproteobacteria Deltaproteobacteria and Epsilonproteobacteria Other Major Lineages of Bacteria and the Archaea

This book provides an overview of bioinspired metal-sulfur catalysis by covering structures, activities and model complexes of enzymes exhibiting metal sulphur moieties in their active center.