Significance of the Double Bond in the Acyl Chain of Cardiolipin Revealed by the Partial Unfolding Dynamics of Cytochrome c Using Femtosecond Transient Absorption Spectroscopy

Abstract

Cytochrome c (Cyt c) released from the mitochondrion acts as a trigger for the onset of apoptosis in which a double bond of cardiolipin (CL) is oxidized upon interaction with Cyt c. To understand the interaction dynamics of Cyt c with the double bond of CL, CLs having acyl chains with a systematic increase in the number of double bonds, 0 (18:0 CL), 1 (18:1 CL), and 2 (18,2 CL), were complexed with Cyt c, and their excited-state dynamics were studied using femtosecond time-resolved pump-probe spectroscopy. Steady-state and femtosecond transient absorption spectra revealed a systematic increase in the partial unfolding of Cyt c with an increase in double bonds in CL, as observed by the enhanced fluorescence intensity and lifetime of tryptophan due to variations in the resonance energy transfer and extended global conformational relaxation time constants. These studies reflect the significance of occurrence of global conformational changes of Cyt c by structural modification near the double bond of CL in the Cyt c-CL complex, which could be prerequisites for the apoptosis.