378 R. LUMRY AND J. D. SPIKES 



both ill the form of a rectangular hyperbola (F vs. /) and in a linear 

 form (I/V vs. /), where V is the Hill reaction rate and / is the relative 

 light intensity. In order to illustrate the precision which can be ob- 

 tained, the slopes and intercepts as calculated by the method of least 

 squares for the eight sets of data in Fig. 1 are given in Table F It will 

 also be noted that equation 2 sets very stringent reciuirements upon 

 any kinetic mechanism proposed to explain the Hill reaction. These 

 restrictions will be discussed in another paper. 



TABLE I. Slopes ( 1/^d) and Intercepts (1//;^) Defined as Given in Equation 2 and 

 Calculated by the Method of Least Squares from the Same Data Which Are 

 Plotted as Means in Fig. 1. Each Set of Data Consisted of Rate Measurements at 



Eight Different Light Intensities 



Data Set Slope 



EFFECTS OF HILL OXIDANTS ON THE HILL REACTION 



A wide variety of compounds will serve as electron acceptors for 

 the Hill reaction of isolated chloroplasts. Considerable work has been 

 carried out in attempts to define precisely the kinetics of the Hill reac- 

 tion in relation to oxidant properties and reaction conditions. Mehler 

 and Brown (5) have shown that dissolved oxygen, a product of the 

 Hill reaction, will also act as an oxidant. Oxygen at ordinary partial 

 pressures cannot compete for electrons to a measurable extent in the 

 presence of the usual oxidants such as ferricyanide and benzoquinone. 

 It can, however, compete with a few substances such as chromate and 

 cause an apparent decrease in the rate and an apparent alteration 

 of the stoichiometry of the Hill reaction. On the other hand, oxygen, 

 even in trace amounts, may complicate experiments through its par- 

 ticipation in a rapid back-oxidation of Hill oxidants after they are 



