Absorption and circular dichroism spectra of chloroplast membrane fragments from spinach,barley and a barley mutant at room temperature and liquid nitrogen temperature

The absorption and CD spectra of chloroplast fragments from spinach, barley and a barley mutant (chlorophyll b-minus) were studied at temperatures of 23°C and ?196°C. The CD spectrum of wild type barley and spinach at ?196°C showed troughs at 640, 653, 676 and 695 nm and a maximum at 667 nm. The CD spectrum of the barley mutant at ?196°C consisted of a large trough at 684 nm, a small trough at 695 nm and a positive peak at 670 nm. A new feature observed at ?196°C but not at 23°C is the trough at 640 nm. This 640 nm CD signal is missing in the CD spectrum of the barley mutant. It is attributable to the light-harvesting chlorophyll $\text{a}\text{b}$ protein which appears to be missing in the mutant. Another new feature, the trough at 695 nm, was observed in the CD spectra of spinach, barley and the barley mutant at ?196°C. The 695 nm trough appears to be sensitive to detergents and it may be due to a labile chlorophyll a·protein complex. Possible interpretations of these data are discussed.