IR REFLECTION-ABSORPTION SPECTROSCOPY - A VERSATILE TOOL FOR STUDYING INTERFACIAL ENZYMATIC PROCESSES

The hydrolysis of the naturally occurring L-enantiomer of 1,2-dihexadecanoyl-sn-glycero-3-phosphocholine (L-alpha-DPPC) by phospholipase A(2) was monitored by means of infrared reflection absorption spectroscopy (IRRAS). The continuing hydrolysis is indicated by a decrease in the intensities of the C=O stretching Vibration of the ester bonds as well as by a decrease in the intensities of the anti-symmetric and symmetric methylene-stretching vibrations. Simultaneously, new bands appear at 1562 and 1542 cm(-1), and at 1578 cm(-1), which represent the formation of an ionic calcium hexadecanoate complex and, presumably, a vibration of peptide structure entities of the enzyme, respectively. Thus the key steps of this enzymatic reaction can be monitored and the specific interactions between the subphase and monolayer constituents can be described in more detail.