[' ', ' ', '“ff', ' ', ',', 'ROLE', 'OF', 'PHOSPHATIOYL', 'SERINE', '291', 'not.', 'been', 'possible', 'to', 'Kencnarewun', 'any', 'hydrolysis', 'of', 'the', '.~', 'PS~ester', 'by', 'the', 'membrane', 'preparation', 'under', 'the', 'experimental', '“conditions', 'for', 'opiate', 'binding.', 'As', 'is', 'discussed,', 'however,', 'the', 'number', 'of', 'membranous', 'PS', 'molecules', 'involved', 'in', 'receptor', 'bind-', 'ing', 'is', 'extremely', 'small.', 'Therefore,', 'the', 'possibility', 'of', 'hydrolysis', 'cannot', 'be', 'excluded.', 'Another', 'explanation', 'for', 'the', 'effectiveness', 'of', 'the', 'PS-ester', 'is', 'that', 'the', '-PO™', 'is', 'still', 'available', 'for', 'interaction', 'with', 'either', 'the', 'opiate', 'or', 'protein,', 'since', 'the', '-C=O', 'groups', 'of', 'the', 'ester', 'are', 'capable', 'of', 'forming', 'H', 'bonds', 'with', 'the', '“NH', 'group.', 'In', 'the', 'studies', 'dealing', 'with', 'the', 'ability', 'of', 'phospholipids', 'to', 'restore', 'opiate', 'binding', 'after', 'inhibition', 'with', 'CTAB,', 'PS', 'was', 'effective', 'while', 'the', 'PS-ester', 'was', 'not', '(Table', '6).', 'Such', 'a', 'dif-', 'ference', 'supports', 'the', 'argument', 'that', 'the', '-COO”', 'group', 'of', 'PS', 'is', 'required', 'for', 'interaction', 'of', 'the', 'bound', 'CTAB,', 'and', 'although', 'it', 'favors', 'the', 'hypothesis', 'that', 'the', 'PS-ester', 'was', 'not', 'hydrolyzed,', 'it', 'is', 'still', 'conceivable', 'that', 'the', 'extent', 'of', 'hydrolysis', 'was', 'insufficient', 'to', 'overcome', 'the', 'effect', 'of', 'CTAB.', 'Nevertheless,', 'the', 'evidence', 'to', 'date', 'favors', 'the', 'hypothesis', 'that', 'the', 'PS-ester', 'itself', 'enhances', 'opiate', 'binding;', 'therefore,', 'the', 'molecular', 'configuration', 'of', 'the', 'endogenous', 'receptor', 'complex', 'has', 'not', 'been', 'altered', 'by', 'the', 'presence', 'of', 'the', 'ester.', 'EFFECT', 'OF', 'CROSS-LINKING', 'OF', 'AMINO', 'GROUPS', 'ON', 'OPIATE', 'BINDING', 'By', 'means', 'of', 'the', 'reagent', 'difluorodinitrobenzene', '(DFDNB),;', 'the', 'amino', 'groups', 'of', 'PS', 'and,', 'to', 'a', 'lesser', 'extent,', 'PE', 'can', 'be', 'cross-linked', 'to', 'neighboring', 'phospholipids', 'and', 'proteins', 'with-', 'in', 'the', 'erythrocyte', 'membrane', '(10).', 'In', 'our', 'laboratory', 'it', 'has', 'been', 'recently', 'demonstrated', 'that', 'synaptic', 'membranes', 'undergo', 'the', 'same', 'kinds', 'of', 'lipid-lipid', 'and', 'protein-lipid', 'interactions', 'observed', 'for', 'erythrocyte', 'ghosts', '(10).', 'After', 'the', 'exposure', 'of', 'neural', 'membranes', 'to', '100', 'uM', 'DFDNB', 'stereospecific', 'opiate', 'bind~', 'ing', 'of', '3H-DHM', 'was', 'decreased', 'to', '74%', 'of', 'the', 'control', '(Table', '7).', 'Furthermore,', 'upon', 'the', 'addition', 'of', 'PS', 'to', 'the', 'DFDNB-treated', 'membranes,', 'there', 'is', 'no', 'enhancement', 'of', 'opiate', 'binding.', 'One', 'interpretation', 'of', 'these', 'observations', 'is', 'that', 'the', 'cross-linking', 'of', 'phospholipids', 'to', 'one', 'another', 'and', 'to', 'proteins', 'resulted', 'in', 'either', 'a', 'partial', 'structural', 'alteration', 'in', 'the', 'receptor', 'complex', 'or', 'in', 'restricting', 'the', 'availability', 'of', 'PS', 'in', 'the', 'vicinity', 'of', 'the', 'complex.', 'The', 'fact', 'that', 'exoge-', 'nous', 'PS', 'did', 'not', 'enhance', 'binding', 'after', 'cross-linking', 'would', 'indicate', 'that', 'either', 'PS', 'could', 'not', 'penetrate', 'the', 'membrane', 'or', 'gain', 'access', 'to', 'the', 'binding', 'site,', 'Possibly', 'because', 'of', 'the', 'inability', 'to', 'exchange', 'with', 'endogenous', 'Phospholipids.', 'It', 'has', 'been', 'shown', '(10)', 'that', 'the', 'erythrocyte', 'membrane', 'becomes', 'refractory', 'to', 'hypotonic', 'lysis', 'after', 'exposure', 'to', 'cross-linking', 'Yeagents.', 'Furthermore,', 'the', 'reagents', 'tend', 'to', 'decrease', 'the', 'permeability', 'of', 'the', 'membrane', 'to', 'anions', '(11).', '0', 'ELOSZtTo00', 'ay']