THE NATTTRAL STATE OF rROTOCHT.OROPHYIX 471 



chlorophyll absorptions makes it clear that the protochlorophyll holo- 

 ehromc was associated with the leading sedimentation boundary and 

 was separated from much of other luaterial in the dialyzed (wtracl 

 by the high-speed centrifugation procedure. 



These facts are significant because they demonstrate that the 

 protochlorophyll holochrome can be removed from the plants in an 

 acti\'e form which does not require soluble cof actors for its function- 

 ing. 



The spreading of the l)oundary associated Avith the protochloro- 

 phyll holochrome during sedimentation was not extensive and ap- 

 peared to be symmetrical, which indicated no obvious heterogeneity 

 in particle size. The sedimentation coefficient (soq) obtained for sev- 

 eral preparations and measured at different stages of preparation 

 ranged from 15.3 to 10.2 Svedbergs. The latter value is probably close 

 to the hypothetical S2n at infinite dilution because (a) the concen- 

 tration of active material, although unknown, was very low, and 

 (6) artificial sharpening of the boundary could not be demonstrated. 

 Comparison of the S20 values with those published for various globu- 

 lar proteins suggests that the molecular weight of the protochloro- 

 phyll holochrome is about half a million. This estimate is subject to 

 revision when the other necessary physical constants of the puri- 

 fied particles are obtained. It has been shown that the active par- 

 ticles pass a Millipore Filter which was rated to pass particles less 

 than 0.43 /x in diameter. 



One more observation on natural protochlorophyll will be related. 

 During the past year it was found that the protochlorophyll in the 

 leaf is composed of both esterified and unesterified (chlorophyllide) 

 components. Both are transformed by light to the corresponding 

 chlorophyllous derivatives (9). After transformation of the chloro- 

 phyllide component to chlorophyllide a, esterification to chlorophyll 

 a takes place quickly. Thus two paths exist in the normal leaf for the 

 formation of chlorophyll for which the following two schemes are 

 suggested : 



1). Protoohlorophvllide +Phytyl Protochlorophyll +Light Chlorophyll a 

 Holochrome > Holochrome > Holochrome 



2). Protochlorophvllide + Light Chlorophyllide a +Phytyl Chlorophyll a 

 Holochrome > Holochrome > Holochrome 



The first of these has already been proposed by Granick (10). 



