Specific helium-neon laser sensitivity of the purified cytochrome c oxidase

Purpose: In order to gain some insight into the mechanism of interaction be tween Helium-Neon (He-Ne) laser light and mitochondrial cytochromes, the se nsitivity of cytochrome electron transfer activity to He-Ne laser was teste d. Materials and methods: Irradiation of solutions containing either purifi ed cytochromes or dissolved rat liver mitochondria was carried out (wavelen gth 632.8 nm, fluence rate 10mW cm(-2), fluence 2 J cm(-2)); the irradiatio n conditions were the ones able to affect cytochrome c oxidase (COX) activi ty in mitochondria (Pastore et at, 1994). Results: Cytochrome c oxidation catalysed by COX was affected by He-Ne lase r irradiation of the purified enzyme. This result was obtained from measure ments of the pseudo-first-order kinetic constant and from determinations of the turnover number of the enzyme, performed at different cytochrome c/COX ratios. Consistently, the kinetic parameters of COX changed. On the contra ry, no alteration in the rate of electron transfer catalysed by either cyto chrome c or bc(1) complex was found. Conclusions: This study shows that purified COX is a specific target of He- Ne laser light; therefore, COX may be considered to be a mitochondrial phot o-acceptor.