SimnlIrv(11'. 1lii order to avoid the l)roblelll of ani uncouplinig effect in stimiiulatioln of potential Hill reaction activity durinig extractioln with heptane, Hill reaction activity was measured with uncouple(d spinach chloroplasts. TI'he reactions were also runi ulnder aerobic coniditionis. Under these conditions a correctioni for a 3(p-chloroph'enyl) -1. 1-dimethylurea insensitive, photos...

Isolated chloroplasts which are incapable of causing a net reduction of COZ accompanied by 02 evolution can still cause a Hill reaction, that is, a photoreduction of an added oxidant with concomitant evolution of a stoichiometric amount of OZ. The occurrence of the Hill reaction has long been regarded as part of the evidence for the conclusion that the action of light in photosynthesis leads fi...

The Hill coefficient is commonly used to estimate the number of ligand molecules that are required to bind to a receptor to produce a functional effect. However, for a receptor with more than one ligand binding site, the Hill equation does not reflect a physically possible reaction scheme; only under the very specific condition of marked positive cooperativity does the Hill coefficient accurate...

Oxidation-reduction reactions in chloroplasts were first 01 served when Hill (1) discovered photolysis by isolated chloro plasts. In the Hill reaction electron transport proceeds from water to the artificial oxidant which can be any one of a number of compounds (24). A cyclic series of oxidation-reduction reactions is postulated as the basis for photosynthetic phosphorylation by spinach chlorop...

In 1939, Hill (1) reported the fundamental discovery that isolated chloroplasts possess the ability to affect a portion of the over-all reaction of photosynthesis; namely, the photolysis of water. In the original experiments of Hill, ferric oxalate was used as the hydrogen acceptor. During the past 20 years, a variety of substances has been found to function as oxidant for the Hill reaction (2)...

Dependence of Hill reaction (ferricyanide reduction) by isolated (broken) chloroplasts on bicarbonate ion increases with time of illumination (upto 4 min) in HCC>3~ free reaction mixture. The stimulation caused by HCOs" is independent of light intensity down to very low intensities indicating an involvement of this ion in early photochemical events of photosystem II. Oxygen evolution was found ...

In the Mehler reaction, a Hill reaction utilizing molecular oxygen as the electron acceptor, rates of net oxygen uptake are stimulated by added manganous ions. Both whole cell photosynthesis and the Mehler reaction are inhibited by copper. Copper inhibition of the Mehler reaction can be reversed by manganese salts. Glutathione. which alone has no effect on Mehler reaction rates, enhances the ef...