A POSSIBLE CALCIUM-BINDING SITE IN D-1 PROTEIN - A FLUORESCENCE AND FTIR STUDY OF THE INTERACTION BETWEEN LANTHANIDES AND A SYNTHETIC PEPTIDE

A peptide ranging from residue 229 to 240 of the D-1 protein of Photos ystem (PS) II was synthesized and lanthanides were used as candidates of calcium. Fluorescence and FTIR spectroscopy were used to test the c onformational adaptation after lanthanide additions. Fluorescence spec troscopy showed that the synthetic peptide provides lanthanide binding site, and that glutamic acids are involved in lanthanide binding. Res olution enhancement techniques were combined with band curve-fitting p rocedures to quantitate the FTIR spectral information from the amide 1 bands. The relative areas of these component bands indicate that lant hanide induced a substantial decrease in the amount of unordered struc ture and turns, while a corresponding increase in the amount of a-heli x and 'open loop' was also observed. This indicates that a relatively compact structure of the synthetic peptide is formed if lanthanides ar e applied. The results may reflect on the physiological and biochemica l function of calcium in PS II, including preventing D-1 from trypsin digestion.