CONTENTS XXV 



7.3 Porphyrin Synthesis in Microorganisms 631 



7.3.1 Porphyrin Synthesis in Bacteria 631 



7.3.'^ Porphyrin Synthesis in Yeast 632 



8 Synthesis of the Porphyrin Nucleus 632 



8.1 Previous Theories 632 



8.2 Attempts at a New Theory of Porphyrinogenesis 637 



8.2.1 Precursors and Mechanism 637 



8.2.2 Ratio of Type I to Type III Porphyrins 643 



XIV. Pyrrole Pigments in Evolution 647 



1 Introduction • 647 



2 Paleontology of Porphyrins 648 



3 Primitive Pyrrole Pigments 649 



4 Respiratory Hematin Enzymes 651 



5 Hematin Pigments of Unknown Function 653 



Bibliography 655 



Subject Index 727 



Appendix: Absorption Spectra Data for Oxyhemoglobin, Hemoglobin, 



Hemoglobin, Carboxyhemoglobin, and Hemiglobin Cyanide 747 



