▁now ▁been ▁expanded ▁to ▁other ▁prote ins ▁in ▁the ▁cell . ▁On ▁the ▁other ▁hand , ▁short ▁p uls es ▁of ▁in hib itors ▁of ▁synth esis ▁of ▁these ▁prote ins ▁results ▁in ▁phase ▁sh ifts ▁of ▁the ▁circ ad ian ▁rh ythm , ▁either ▁del ays ▁or ▁adv ances , ▁depending ▁when ▁the ▁pul se ▁is ▁admin ister ed . ▁At ▁still ▁another ▁level , ▁protein ▁ph osph ory lation ▁in hib itors ▁also ▁influence ▁the ▁period ▁of ▁the ▁rh ythm . ▁ ▁Other ▁lum ines cent ▁systems : ▁Early ▁in ▁his ▁career ▁H ast ings ▁developed ▁techniques ▁to ▁quant ify ▁the ▁level ▁of ▁o xygen ▁required ▁in ▁a ▁lum ines cent ▁reaction ▁for ▁several ▁different ▁species ▁including ▁b acter ia , ▁fung i , ▁fire f lies ▁and ▁ost rac od ▁cr ust ace ans . ▁This ▁work ▁showed ▁that ▁o xygen ▁g ating ▁is ▁the ▁mechanism ▁for ▁fire fly ▁flash ing . ▁In ▁other ▁work ▁when ▁he ▁was ▁in ▁the ▁Mc El roy ▁lab ▁he ▁exam ined ▁the ▁basic ▁bio chem ical ▁mechanism ▁of ▁fire fly ▁luc ifer ase ▁and ▁demonstrated ▁that ▁co enz yme ▁A ▁stim ul ates ▁light ▁emission . ▁His ▁lab ▁first ▁demonstrated ▁that ▁the ▁green ▁in ▁v ivo ▁co el enter ate ▁bi ol um ines c ence ▁occurs ▁because ▁of ▁energy ▁transfer ▁from ▁the ▁lum ines cent ▁mole c ule ▁( a equ or in ), ▁which ▁alone ▁em its ▁blue ▁light , ▁to ▁a ▁secondary ▁green ▁em itter ▁which ▁they ▁term ed ▁green ▁flu