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 F1 using infrared spectroscopy. Our results show that in the absence of added nucleotides this complex contains similar percentages of alpha-helices, beta-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 decrease in beta-structure and an increase in alpha-helix and reverse turns. The effect of nucleotide binding on the thermal stability of F1 was also studied; the thermal denaturation temperature, 55 degrees C, was increased by 11 degrees C and 7 degrees C by ATP and ADP, respectively. These results indicate that nucleotide binding affects the secondary structure of F1, stabilizing the complex.