Interaction of phospholipid with brain glutamate decarboxylase

Abstract

Porcine brain glutamate decarboxylase interacts with derivatized phopholipid fluoreceine-dipalmitoyl phosphatidyl ethanolamide(FL-DPPE). Upon addition of the enzyme to FL-DPPE, an increase in fluorescence intensity is discemible, together with an increase in emission anisotropy. Judging from anisotropy values, FL-DPPE is rapidly trapped by the protein matrix. The binding of FL-DPPE to glutamate decarboxylase induces aggregation of the dimeric enzyme into polymeric species. It appears that 2.2 mol of FL-DPPE are bound per protein molecule as determined by a study of fluorescence quenching. A quenching bimolecular rate contant of 1.1 X 109M-1·S-1 was obtained from a Stem-Volmer plot. These results suggest that fatty acid tails serve as anchoring sites for the protein dimers, whereas the fluorescent probe covalently bound to the hydrtphilic head of the phospholipid, remains accessible to the collisional quencher.