28 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



EQUIPMENT 



The Beckman DU spectrophotometer, with photomultiplier and adapter, 

 was used in most of our 230 m/x experiments. The amplified output of the 

 photomuhijilicr is fed through a 60 cps synchronous chopper and then 

 further amphfied about five hundred times. This amplified output is dis- 

 played both on the oscilloscope and on the Bruel-Kjaer recorder. For these 

 experiments at 230 m/x, a Beckman hydrogen arc was used as the light 

 source; its stability was more than sufficient for most experiments. The 

 temperature in the cuvettes was controlled by coils surrounding the cu- 

 vettes. For measurements made at other than room temperatures, a cop- 

 per const antin thermocouple was inserted next to the cuvettes before and 

 after each reading. 



A typical recorded curve is shown in figure 2. The width of the line is 

 due to the recorder pen partially following the sixty cycle signal. The 



standord 



•.Z7 cl 



current HgOg + 1-23 x lO'' M catolose 



dork current 



Stondord 



Fig. 2. A typical record at 230 m/j.. 



stability was checked in each case by recording the dark current level, 

 and the optical density of a solution in a comparison silica cuvette. At 

 the arrow, 0.02 ml of a 0.22 /am solution of catalase was stirred into the 

 HoOo in the cuvette. Experiments showed that the half time, ti/o , for this 

 reaction is independent of the exact H0O2 concentration, but inversely 

 proportional to the enzyme concentration. In order to obtain meaningful 

 curves it was found necessary to have the enzyme solution at the same 

 viscosity and temperature as the peroxide solution. A difference in vis- 

 cosity of a few centipoise changed the optical density more than the 

 change due to the hydrogen peroxide disappearing. 



The build-up of p to pi takes place in a very much shorter period of 

 time. To observe this it is necessary to use a flow system. A thermistor is 

 used as the sensing element to activate a magnetic amplifier which regu- 

 lates the temperature of the liquid in the control coils. An accessory con- 

 trol system regulates the temperature in the coils surrounding the ob- 

 servation chamber. The temperature of the reactants entering the flow 

 system is monitored continuously with a copper constantin thermocouple. 



The optical density in the observation tube could be followed either 



