Carbon Dioxide & the Hill Reaction.

Recently a i uniber of investigators have reported that the Hill reaction is mior-e ral)i(l in the plreelice of CO., thiani in its absence. However., thle phenome1on1 (it CO., dependence can only Ie (lemonstrated un(ler certain conl(litioiis and it is thlerefore regrettable that there hlas beenino agreement as to the nlattire of these cond(litions. \Warburg an(l Kiippahl ( 9) haxve stresse(l the iniportaince of preillumiinatinig the chlioropllasts. whereas Abeles et al. (1) foulid the effect primarily in unbufferedl nedia. Stern anid Vennesland, on the othier han(l, observe(l large CO., effects in butfered niie(lia cand( without preillumination: in thieir stu(dies the composition of the buffer xvas imiiportant ( 7 ) \Ve have con fir-mie(d and extendledl the obls ervations of the last-named authors. \\e have ailso invxestigate(l the relati,on of CO., elpendlence to lighit intensity, the state of uncouplilig of the pliosiPhorvlation system, ain(l the niattul-e of the Hill reatctionl oxidant. The new information l)resenitedl her-e provides little support for \Warburg's contenitioni that CO, pllaYs a role in the Hill reaction atkin to its role ini pihotosynthesis. In fact it is inconsistent with somile of the (letails of Warburg's p)ostulate(l miechiaiisin. Ho ever, the crucial (Iuestioln reniais Uniswere(l: Is CO.) a metabolite in tile Hill reaction (Or are We (lealiig with ind(lirect and possibly ulispecific effects of the bicar-b-onate ion ?