430 PHOTOMECHANICAL CONSIDERATIONS 



filled with solvent. The loaded cell was centrifuged for 24 hours at 

 20,410 rpm, and the equilibrium distribution of material in each sample 

 compartment determined by photographing the interference patterns 

 resulting from the index of refraction gradients in each compartment 

 (see Fig. 6). The fringe shift at any point is directly proportional to 

 protein concentration. The magnitude of the fringe shift (and thus, the 

 relative concentration) was measured at regular intervals in each 

 compartment, and the logarithm of the displacement was plotted versus 

 the distance from the center of rotation as in Fig. 7. The molecular 

 weight was calculated from the slope of the best straight line fitting 

 the experimental points according to the equation 



Jr (X- Vp) ^' 



V was assumed to have a value of 0.74, The calculated values of mole- 

 cular weight from the three compartments ranged from 1.31 to 1,42 

 X 10"^ and gave an average value of (1,37 ± ,05) x 10^. 



The diffusion coefficient at infinite dilution and 20°C, calculated 

 from the sedimentation coefficient and molecular weight, is about 

 5 X 10"'^ cm2/sec. 



CHLOROPHYLL-TO-PROTEIN RATIO 



A preliminary estimate of the magnesium content of the protein- 

 chlorophyll complex has been made by emission spectrography. The 

 intensity of the Mg emission line(s) from a solution having an absorb- 

 ancy of 3,0 cm-1 at 809 m^ indicated a Mg concentration of 8.8 x 10"^ 

 M after correction for the Mg in the buffer against which the sample 

 had been dialyzed. This level of magnesium corresponds to an absorb- 

 ancy index of 3,4 x 10^ M-l cm"! at 809 ra^i based on chlorophyll, if 

 the Mg- to- chlorophyll ratio is assumed to be unity. 



A preliminary estimate of the nitrogen content has been made by 

 micro-Kjeldahl analysis (12). A solution having an absorbancy of 4.6 

 cm"l at 809 m/i had a nitrogen content of 0.045 g/1. Protein concentra- 

 tion was estimated to be 0,28 g/1 on the assumption of a nitrogen con- 

 tent of 16%, 



From the magnesium and nitrogen determinations, the minimum 

 value of the chlorophyll-to-protein ratio is estimated to be 4,8 x 10"^ 

 mole chlorophyll per gram protein. For a unit of 1,4 x 10^ molecular 

 weight, this means a minimum of six bound chlorophyll groups. 



