An exceptional example of photocatalytic protein bioconjugation involves using a quinolinone chromophore-based photocatalyst to accelerate the thiol-ene reaction between Cys and terminal olefins through hydrogen-atom transfer catalysis. Activation of electrophilic species employing SET and combinations of SET and hydrogen atom transfer (HAT) for Cys modification and histidine (His) modification 72 are also noteworthy.