INFLUENCE OF NUCLEOTIDES ON THE SECONDARY STRUCTURE AND ON THE THERMAL-STABILITY OF MITOCHONDRIAL F1 VISUALIZED BY INFRARED-SPECTROSCOPY

We have studied the secondary structure of mitochondrial F-1 using inf rared spectroscopy, Our results show that in the absence of added nucl eotides this complex contains similar percentages of alpha-helices, be ta-structures and reverse turns (30%, 28% and 31%, respectively), The influence of ADP and ATP on the different types of secondary structure was determined; when all the nucleotide-binding sites were occupied, small but reproducible changes were observed, corresponding to a decre ase in beta-structure and an increase in alpha-helix and reverse turns . The effect of nucleotide binding on the thermal stability of F-1 was also studied; the thermal denaturation temperature, 55 degrees C, was increased by 11 degrees C and 7 degrees C by ATP and ADP, respectivel y. These results indicate that nucleotide binding affects the secondar y structure of F-1, stabilizing the complex.