VISCOSITY AND REACTION RATES IN BACTERIA 361 



The reaction rates are evaluated by tangents to the linear portions 

 of the cytochrome oxidation and reduction kinetics. Since relative 

 rates are of interest here, slopes in millimeters of vertical deflection 

 per millimeter horizontal deflection may be employed, although con- 

 version to molar rates is employed in Fig, 3(b). 



In Fig, 2b, the same technique is used in recording the light- 

 induced reaction in the same Chromatium suspension which has been 

 diluted with two parts of glycerol to a final concentration of 67 per 

 cent. The kinetics of cytochrome oxidation on illuminating the sus- 

 pension are rather similar to those in Fig, 2A, A remarkable differ- 

 ence in the two traces is the slow cytochrome reduction in the glycerol- 

 treated cells; at least 0.4 second is required for half-maximal effect. 



In Fig. 3, A and B, are plotted the results of two series of experi- 

 ments on the effect of glycerol upon the light-induced response of 

 cytochrome of type c in different suspensions of Chromatium. In both 

 figures are represented the initial slopes of the light responses, to- 

 gether with the reciprocal of the time for half-maximal rise on illumi- 

 nation (rapid phase only) as well as the reciprocal of the time for half- 

 maximal fall on cessation of illumination. Lastly, both graphs show 

 the absorbancy increment on illumination. Fig. 3A covers the range 

 to 67 per cent glycerol and Fig. 3B covers the range to 80 per cent 

 glycerol. Considering Fig. 3A, we observe that the initial rate of ab- 

 sorbancy change on illumination is more rapid in the presence of 

 glycerol and that observed on cessation of illumination is less rapid. 

 Also the increment of absorbancy on illumination increases with in- 

 creasing glycerol concentration. K, however, we measure the recipro- 

 cals of the times for half-maximal response, it is noted that the light- 

 on response decreases 30 per cent at 40 per cent glycerol but remains 

 constant thereafter. However, the reciprocal of the half-time "off" 

 falls 87 per cent at 67 per cent glycerol. It should be pointed out that 

 half-times for these reactions are sometimes difficult to measure be- 

 cause the traces are occasionally diphasic and more reliance is placed 

 on the initial rates. 



In Fig. 3B, it was possible to cover a wider range of glycerol con- 

 centration and it is seen that the initial slopes again diverge with the 

 glycerol concentration; a 3:1 ratio of initial rates is obtained at 67 per 

 cent glycerol. In this experiment the reciprocal of the time for half- 

 maximal response to illumination is approximately independent of 

 glycerol while the response to cessation of illumination drops pre- 

 cipitously at 80 per cent glycerol. Again the illuminated minus dark 

 steady state change suggests an increased steady state oxidation of 

 cytochrome component. 



Both these results are consistent with a lack of inhibition of the 

 light-induced response in Chromatium in the presence of a wide range 

 of glycerol concentrations. The "initial slope" data further suggest that 

 the light-induced oxidation of cytochrome proceeds more rapidly in the 



