The Porphyrin Handbook, Volume 13: Chlorophylls and Bilins: Biosynthesis, Synthesis, and Degradation provides information pertinent to every aspect of the chemistry, synthesis, spectroscopy, and structure of phthalocyanines. This book examines the biology and medical implications of porphyrin systems. Organized into eight chapters, this volume begins with an overview of magnesium chelatase as a complex enzyme involved in the biosynthesis of chlorophyll and bacteriochlorophyll. This text then provides an accurate historical review of the two enzymes involved in photosynthetic pigment production. Other chapters consider the processes that take place in darkness in all plants including angiosperms as the early steps of chlorophyll biosynthesis. This book discusses as well the reactivity and structures of the known chlorophyll catabolites from vascular plants, synthetic sources, and microorganisms. The final chapter deals with the methodologies used for the synthesis of bile pigments. This book is a valuable resource for research scientists, engineers, and clinicians.

The production of chemical energy from light energy is arguably the most important reaction known. Nearly all life depends on energy derived from light and it is by this process that the atmosphere of our planet was oxygenated. Chlorophyll is the pigment that absorbs light and donates an electron initiating the process of photosynthesis. This highly complex molecule is the result of many chemical reactions collectively known as chlorophyll biosynthesis. Chlorophyll is a modified tetrapyrrole and shares a common synthetic pathway to vitamin B12, Siroheam and haem. Photosynthetic organisms need both chlorophyll and haem, and the branch point they share, committing to the production of either is thought to be highly regulated. The common precursor to both pigments is protoporphyrin IX and the fate of the macrocycle depends on which divalent metal ion is inserted into the tetrapyrrole. The insertion of Fe2+ by ferrochelatase commits to the production of haem whereas the insertion of Mg2+ by magnesium chelatase commits to the production of chlorophyll. The magnesium chelatase is comprised of three subunits that are all essential for activity and are known as ChlH (~150 kDa), ChlD (~75 kDa) and ChlI (~40 kDa). It is known that the H protein binds both the tetrapyrrole substrate and product of the reaction. The I and D subunits are thought to be the catalytic element of the enzyme and once a H•substrate complex is formed, this binds with an ID complex to initiate the reaction. This work will focus on the structural and functional characteristics of a thermophilic magnesium chelatase (from Thermosynechococcus elongatus) which have never been previously studied.

The protein magnesium chelatase consists of three subunits, ChlI, ChlD and ChlH. This protein lies at the branch point between heme and chlorophyll biosynthesis and has a regulatory role. It requires large amounts of energy to insert a magnesium ion into its substrate protoporphyrin IX. Two subunits, ChlI and ChlD are members of the AAA+ ATPase super family of enzymes, and ChlI hydrolyses ATP to drive the introduction of magnesium into the porphyrin ring. Magnesium chelatase (ChlIDH) will catalyse the exchange of radiolabelled ADP to ATP while the metal ion chelation reaction progresses in the for- ward direction. In isolation, the AAA+ ATPase subunit, ChlI, also catalyses the same reaction. In contrast radiolabelled orthophosphate (Pi) cannot ex- change to form ATP. This suggests a mechanism where either no E.ADP complex exists or it unable to react with free phosphate to give ATP. Mutations in the putative conserved ATPase site in ChlI show MgATP2- is hydrolysed in a stochastic manner, while cooperativity between subunits promotes MgATP2- binding. Similar mutations in the putative ATPase site in ChlD reveal the first functional role of this enzyme in allosteric control of magnesium chelatase activity.