1 Assay of Phospholipases.- 1.1. General Considerations and Choice of Assay.- 1.1.1. Physical Form of Substrate.- 1.1.2. Liposomes.- 1.1.3. Emulsions.- 1.1.4. Monomolecular Films.- 1.1.5. Natural Cellular Membranes.- 1.1.6. Lipoproteins.- 1.2. Methods of Assay.- 1.2.1. Titration.- 1.2.2. Colorimetric and Fluorimetric Assays.- 1.2.3. Assay Employing Radiolabeled Substrates.- 1.2.4. Preparation of Fatty Acyl-Labeled Phospholipids.- 2 Bacterial Acyl Hydrolases (Phospholipases A, B, and Lysophospholipases).- 2.1. General Considerations.- 2.1.1. Escherichia coli.- 2.1.2. Bacillus megaterium.- 2.1.3. Mycobacterium phlei.- 2.1.4. Acyl Hydrolases of Genus Vibrio.- 3 Bacterial Phosphodiesterases (Phospholipases C and D).- 3.1. General Considerations.- 3.1.1. Genus Clostridium.- 3.1.2. Bacillus cereus.- 3.1.3. Staphylococcus aureus.- 3.1.4. Acinetobacter.- 3.1.5. Streptomyces hachijoensis.- 3.1.6. Genus Pseudomonas.- 3.2. Bacterial Phospholipases D.- 3.2.1. Genus Corynebacterium.- 3.2.2. Genus Streptomyces.- 3.2.3. Haemophilus parainfluenzae.- 3.2.4. Other Gram-negative Bacteria.- 3.2.5. Vibrio damsela.- 3.3. Summary.- 4 Other Microorganisms.- 4.1. General Comments.- 4.2. Penicillium notatum.- 4.3. Saccharomyces cerevisiae.- 4.3.1. Acyl Hydrolases (Phospholipase B).- 4.3.2. Phosphodiesterases (Phospholipases C and D).- 4.4. Amoebic Phospholipases.- 4.4.1. Naegleria fowleri.- 4.4.2. Acanthamoeba.- 4.5. Tetrahymena pyriformis.- 5 Plant Phospholipases.- 5.1. General Considerations.- 5.2. Initial Studies.- 5.3. Purification of Phospholipase D.- 5.4. Transphosphatidylation and Substrate Specificity.- 5.5. Factors Regulating Phospholipase D Action.- 5.6. Function of Plant Phospholipases D.- 6 Cellular Phospholipases Al and Lysophospholipases of Mammals.- 6.1. General Introduction to Cellular Phospholipases from Mammals.- 6.2. Phospholipase A1: General Considerations.- 6.2.1. Pancreatic Phospholipases Al.- 6.2.2. Liver.- 6.2.3. Heart.- 6.3. Lysophospholipases: General Considerations.- 6.3.1. Early Observations.- 6.3.2. Adrenal Medulla Lysophospholipase.- 6.3.3. Beef Liver Lysophospholipases.- 6.3.4. Rat Lung Lysophospholipase.- 6.3.5. Amnionic Lysophospholipase.- 7 Phospholipase A2 of Mammalian Cells.- 7.1. General Considerations.- 7.2. Phospholipase A2 of Neutrophils (Polymorphonuclear Leukocytes).- 7.3. Phospholipase A2 of Brain.- 7.4. Phospholipase A2 of Platelet.- 7.5. Phospholipase A2 of Macrophages.- 7.6. Phospholipase A2 of Erythrocytes.- 7.7. Phospholipase A2 of Liver Mitochondria.- 7.8. Phospholipase A2 of Lung Exudate.- 7.9. Phospholipases A2 in Cultured Tumor Cells.- 7.10. Intestinal Phospholipase A2.- 7.11. Heart Phospholipase A2.- 7.12. Spleen Phospholipase A2.- 8 Phospholipases C and Phospholipases D of Mammalian Cells.- 8.1. General Considerations.- 8.2. Mammalian Phospholipases C: Historical Background.- 8.2.1. Heart Phospholipase C.- 8.2.2. Brain Phospholipase C.- 8.2.3. Ram Seminal Vesicle Phospholipase C.- 8.2.4. Rat Liver Phospholipase C.- 8.2.5. Platelet Phospholipase C.- 8.2.6. Lysosomal Phospholipases C.- 8.2.7. Some Aspects of Phospholipase C Regulation.- 8.3. Sphingomyelinases.- 8.3.1. Lysosomal Sphingomyelinase.- 8.3.2. Microsomal Sphingomyelinase.- 8.3.3. Erythrocyte Sphingomyelinase.- 8.4. Phospholipase D.- 8.4.1. Brain Phospholipase D.- 8.4.2. Eosinophil Phospholipase D.- 8.4.3. Lysophospholipase D.- 8.5. Summary.- 9 Pancreatic and Snake Venom Phospholipases A2.- 9.1. General Considerations.- 9.2. Purification, Activation, and Some Characteristics of the Pancreatic Phospholipase A2.- 9.2.1. Purification of Pancreatic Phospholipase A2.- 9.2.2. Activation of the Prophospholipase A2.- 9.2.3. General Characteristics of Pancreatic Phospholipases A2.- 9.3. Snake Venom Phospholipases A2.- 9.3.1. Purification of Snake Venom Phospholipases A2.- 9.4. Structure of the Phospholipases A2.- 9.4.1. Sequence Analysis of Phospholipases A2.- 9.4.2. Crystallographic Studies of Phospholipases A2.- 9.5. Functionality of Amino Acids in Venom and Pancreatic Phospholipases A2: Enzyme Modification.- 9.5.1. Chemical Modification.- 9.5.2. Amino Acid Substitution.- 10 Mechanism of Phospholipase A2 Action.- 10.1. General Considerations.- 10.2. Metal Ion Binding to the Enzyme.- 10.2.1. Venom Phospholipases.- 10.2.2. Pancreatic Phospholipases A2.- 10.2.3. Model of the Ca2+-Binding Loop.- 10.2.4. Bee Venom Phospholipase A2.- 10.3. Phospholipase Substrate Binding.- 10.3.1. General Considerations.- 10.3.2. Interaction with Monomers.- 10.3.3. Interaction with Substrate Micelles.- 10.3.4. Substrates in Mixed Micelles.- 10.3.5. Substrates in Aggregates (Nonmicelle).- 10.3.6. Monomolecular Films of Phospholipid as Substrate.- 10.4 Mechanism of Phospolipase A2 Hydrolysis.- 11 Function of Phospholipases.- 11.1. General Considerations.- 11.2. The Phosphatidylinositol (PI) Cycle and the Arachidonate Cascade.- 11.2.1. Calcium Regulation of Phospholipase C.- 11.2.2. Substrate for the PI Cycle.- 11.2.3. Coupling of Agonist Receptor to Phospholipase C.- 11.2.4. The Arachidonate Cascade.- 11.2.5. Regulation of Phospholipase A2.- 11.3. Phospholipases in Digestion of Dietary Fat.- 11.4. Phospholipases in Lipoprotein Metabolism.- 11.5. Action of Snake-Venom Enzymes.- 11.6. Phospholipases as Structural Probes.- 11.6.1. Phospholipases as Probes of Membranes.- 11.6.2. Analysis of Phospholipid Structure Using Phospholipases.- 11.7. Summary.- References.