Substrate specificity of two cationic lipases with high phospholipase A1, activity purified from guinea pig pancreas II. Studies on glycerophospholipids |
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| Affiliation: | 1. Institute for Collaborative Biotechnologies, University of California Santa Barbara, USA;2. Nutrition Care Division, Madigan Army Medical Center, USA;3. Oak Ridge Institute of Science and Education, USA;4. Nutromics Pty Ltd, Australia;5. Neuroscience Research Institute, Department of Psychological and Brain Sciences, University of California Santa Barbara, USA;6. Biomedical, Electrical, and Chemical Engineering, Director Novel Devices Laboratory, University of Cincinnati, USA;7. Department of Chemistry and Biochemistry, Biological Engineering Graduate Program, University of California Santa Barbara, USA |
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| Abstract: | The substrate specificity of two cationic lipases with high phospholipase a1 activity purified from guinea pig pancreas has been tested towards various natural and synthetic phospholipids. Natural glycerophospholipids carrying a 1-acyl-bond were degraded in the following order of decreasing activity: phosphatidylcholine = phosphatidylinositol > 1-acyl-sn-glycero-3-phosphocholine > phosphatidylethanolamine > phosphatidylglycerol. Sodium deoxycholate was an activator with all the phospholipids tested, each one requiring its own optimal concentration of detergent. Whereas 1-alkyl-2-acyl-sn-glycero-3-phosphocholine remained fully insensitive to enzyme degradation, 2-acyl-sn-glycero-3-phosphocholine was hydrolysed to some extent. However, additional experiments involving time-course hydrolysis revealed that this was entirely due to the migration of the 2-acyl-chain to the sn-1 position. From studies using racemic or enantiomeric phosphatidylcholines, it was concluded that the enzymes are not stereospecific. Activity against 1-acylpropanediolphosphocholine was much lower than with 1-acyl-sn-glycero-3-phosphocholine, indicating that the 2-hydroxyl group (or the 2-acyl-ester group) participates in the substrate reactivity through a strong inductive effect. Some activity could be detected against 1,3-diacylglycero-2-phosphocholine (β-phosphatidylcholine) and 1-acylglycol-2-phosphocholine. It is thus concluded that the failure of the lipases to hydrolyse the 2-acyl-bond in a natural phospholipid is due to the steric hindrance brought about by the acyl, alkyl or hydroxyl group present in the sn-1 position. The lipases might also be unable to hydrolyse acyl-ester bonds involving a secondary alcohol. |
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