Irradiation with a diode at 820 nm induces changes in circular dichroism spectra (250-780 nm) of living cells

A sensitive method for measuring the circular dichroism (CD) of living HeLa cells in the visible-near infrared (IR) region is developed. The changes in CD spectra from 250 to 780 nm of HeLa cell suspension after the first and second irradiation at 820 nm in dose 9 J/cm² are investigated. The CD spectrum of the intact cells is well structured and characterized by a positive signal in the UV (250-290 nm) and visible-near IR (500-780 nm) regions as well as by a negative signal in 300-450 nm region. Distinct maxima in the visible-near IR region are recorded at 566, 634, 680, 712, and 741 nm. As a rule, the peak circular dichroism signals decrease in the irradiated cells except of the area 750-770 nm. Peak positions (except the peak at 680 nm) shift as a rule to the long-wavelength direction. The most remarkable changes in peak positions as well as in CD signals are recorded in the region 750-770 nm: an appearance of the new peak at 767 nm after the first irradiation and its shift to 752 nm after the second irradiation. The peaks at 712 and 741 nm disappear after the irradiation. A new peak appears at 601 nm. It is assumed that the changes in the degree of oxidation of the chromophores of cytochrome c oxidase caused by the irradiation are accompanied by conformational changes in their vicinity. It can be suggested that these changes are occurring in Cu_B environment