Singlet oxygen quenchers and the photodynamic inactivation of E. coli ribosomes by methylene blue

$\text{E. coli}$ ribosomes are readily photoinactivated by methylene blue in the presence of air. A variety of singlet oxygen quenchers like NaN₃, 2,5-dimethylfuran, hydroquinone and ascorbic acid provide about 60% protection against this photoinactivation indicating that a major mechanism of ribosome inactivation proceeds through the formation of singlet oxygen, with small contributions (<40%) from other mechanisms. The singlet oxygen quenchers, 1,4-diazabicyclo 2.2.2] octane and triethylamine give unexpected results, in that they show no protection against photoinactivation.