Introduction ...... 56 Formation of Heme and Chlorophyll Precursors 60 1. b-Aminolevulinic Acid 60 2. Succinate-Glycine Cycle 62 3. Porphobilinogen 63 4. Uroporphyrinogen III 64 5. Coproporphyrinogen III 69 6. Protoporphyrin IX 70 Insertion of Iron into Protoporphyrin IX 71 Cytochromes and Heme Enzymes 72 The Relationship Between Chlorophyll a and Bacteriochlorophyll Biosynthesis ......... 73 General Scheme of Chlorophyll Biosynthesis 74 Intermediates in the Conversion of Protoporphyrin IX to Chlorophyll 76 1. Magnesium Protoporphyrin Monomethyl Ester 76 2. Magnesium Protoporphyrin 77 3. Magnesium 2-Vinylpheoporphyrin a5 Monomethyl Ester 79 Conversion of Magnesium 2-Vinylpheoporphyrin a5 Monomethyl Ester to Chlorophyll a 79 Origin of Chlorophyll b 81 Chlorophylls c and d and Chlorobium Chlorophylls 82 Control Mechanisms of Heme and Chlorophyll Biosynthesis 83 1. Control Through Intracellular Localisation 83 2. Control Through Altered Enzyme Activity 83 3. Control Through Alteration of the Amount of Enzyme Synthesis 85 Control of Hemoglobin Synthesis 86 Literature Cited ... 86