581 



Jerome J, V/olken 



are in a d;;,^Tiamic state, and are arranged so that their ahsorption 

 oscillators are oriented for maximum absorption. 



THE C'JLOROPHYLL-PRaiEIN 



The molecular weight of the chlorophyll-protein in the chloro- 

 plast can be estimated from the chloroplast structural data (Table 

 l), in which the geometry and. chloroph\'ll concentration of the 

 chloroplast is employed. The assumption is that the electron- 

 deixse layers would contain a double layer of protein inacromole- 

 cules, and that there is one chlorophyll molecule per protein 

 molecule. An eq.i;ation can be \jTitten in a form containing only 

 the experimental measurements : 



M = . TcD^sLn 



W 



where D is the length, T is the thickness of the dense layers, s_ 

 is the density talcen as 1,3 that of a protein (if a lipoprotein, 

 the density would be closer to l.l), L is Avogadro's niomber, n is 

 the number of dense layers, and N is the number of clilorophyll 

 raolecviles. The moleculaip weight calcvilated from this equation is 

 of the order of 21,000^^"^/. The molecular weight \ra,s also esti- 

 mated from data talcen from the in vivo Euglena cliloroplast using 

 interference mJ.croscopy, the area of the chloroplast, and its chl- 

 orophyll concentration. 'The calculated molecular \reight obtained 

 iras lo,OOo'-^^-'-°). Frey-V/yssling^-^^^ suggests tlxat the lamellae 

 are globiilar raacromolecules of the order of 65 ^ in diameter (see 

 Fig. 7), which would accauodate I6 chlorophyll molecules with 3. 

 molecular weight of the order of 68,000, These calculations give 

 us an estJjTiate of the minimum molecular weiglit of a chlorophyll- 

 protein molecule, 



CIELOROPLASTIil 



Since the chloroplasts contain large quantities of lipid, it 

 is difficult to solubilize them in ^^ater, IIo\/ever, colloidal sus- 

 pensions of the chloroplasts cem be prepared by ultrasonic tech- 

 niques and by extraction with detergents (digitonin, tergitol). 

 Detergents in solution foiin colloid aggregates, micelles, that 

 liave a very strong attx^ction for many of the more complex dye 

 molecules. The non-ionic re crystallized digitonin (C^cHqqOoo) ^ 

 digitalis glycoside, is a nitrogen-free detergent, ana has a chl- 

 olesteric structure, Digitonin becaiAse of its properties, opens 

 the pigment-lipid, lipoprabe in layers of the cliloroplast and 

 forms chloroplastin iTiicelles^-'-^''. Sedimentation in an anal;;-tical 

 ultracentrifuge, and electrophoresis, .sljo\f that chloroplastin be- 

 lia-ves as a homogeneous micelle system ■■-^'^^, Absorption spectra of 



