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R. A. Olson 



oscillators absorbing at shorter wave lengths may also be identified with the 

 inductive resonance energy acceptance behavior C . 



It appears obvious that an oriented pigment should be related to the or- 

 derly fine structure of the chloroplast lamellae. The interdependence of chloro- 

 phyll and protein in the chloroplast structural array has been demonstrated by 

 1) the dependence of lamellar development on chlorophyll formation and 2) 

 the destructive effect of proteolytic enzymes on the lamellar pigment struc- 

 ture.'^" ' In the chlorophyll-protein complex implied by these and other in- 

 vestigations it would be expected that molecular orientation of pigment would 

 involve molecular orientation of the attached macromolecule. Therefore it 

 should be the orientational aspects of the protein moiety in chloroplasts that com- 

 mand attention rather than those of chlorophyll alone. Dimeric or trimeric 

 forms of chlorophyll contributing to orientation must be compatible with attach- 

 ment sites in the protein. Our present knowledge of the nature of chloroplast 

 protein is quite limited. While the amino acid composition has been recently 

 determined, the sequence is unknown.^ ' Moreover, the polypeptide configu- 

 ration of the chloroplast protein has not been designated. 



Polypeptides can be molecularly oriented in mesophases. In this regard 

 it is of interest to examine some of the mesophase properties of synthetic poly- 

 peptides. Robinson has studied the intrinsic ability of poly-y-benzyl-L-glutamate 

 to form, spontaneously, lamellar structures . (^^' The remarkable likeness of 

 such structures to those in chloroplasts is shown in Plate 11 D. The lamellar 

 spacing depends on concentration, solvent, temperature, etc. , but has a repro- 

 ducible value for any one set of conditions. It may be as large as 100 ^ or too 

 small to be resolved by visual microscopy. Optical anisotropic properties of 

 this lamellar structure indicate it to be a uniaxial system with the optical axis 

 perpendicular to the plane of the lamellae. The optical properties of this struc- 

 ture thereby simulate those of the chloroplast. Optical rotatory measurements 

 indicate the lamellae to be composed of long, parallel helices with a periodicity 

 of rotation of the direction of orientation in successive lamellar planes. By 

 analogy, chloroplast lamellae would be composed of long, parallel polypeptide 

 helices and the orientation of chlorophyll molecules would be governed by avail- 

 able attachment sites. Attempts in our laboratory to adsorb chlorophyll on such 

 mesophase structures were unsuccessful. The polymer is extremely hydropho- 

 bic and the solvents required for its structural development are such excellent 

 solvents for chlorophyll that the pigment resists adsorption. It might be ex- 

 pected that a similar structural array of native, long hydrophilic polypeptide 

 molecules in chloroplasts could be detected optically by measurements of di- 

 chroism in the ultraviolet region. Ruch, however, was unable to detect any 

 ultraviolet dichroism in fixed and extracted chloroplasts and concluded that a 

 globin or spherical protein molecule was involved.' ' In our laboratory we 

 have been unable to detect ultraviolet dichroism in the chloroplasts of living 

 Euglena cells . These observations however, do not automatically preclude a 

 polypeptide helix array in the chloroplast. Perhaps the employment of more 

 refined observation techniques would detect such optical effects in the 

 chloroplast. 



