The Natural State of Protochlorophyll 



JAMES H. C. SMITH, DONALD W. KUPKE,* JOSKF E. LOEFFLER, 

 ALLEN BENITEZ, INGRID AHRNE, and ARTHUR T. GIESE, De- 

 'partment of Plant Biology, Carnegie Institution of Washington, Stanford, 



California 



It is a generally accepted conclusion that chlorophylls when they 

 occur naturally in plants are in a different chemical state than when 

 they are extracted from the plants and dissolved in organic solvents. 

 This conclusion is based on the differences observed in their absorp- 

 tion spectra, in their stability to light, and in their physiological ac- 

 tivities in the two environments. When chlorophylls are extracted 

 from the plant by organic solvents, their spectral absorption shifts to 

 shorter wavelengths and their natural physiological activity is de- 

 stroyed. To account for these differences it has been assumed that 

 the chlorophylls in the native state are combined with carriers to form 

 chemical units possessing characteristic absorption spectra and physi 

 ological activities. For convenience of discussion the complete chemi- 

 cal unit has been called a holochrome (1,2), which term is defined as 

 follows: "Holochrome (Gr. holos whole -\- chroma color) is proposed as 

 a term to designate a colored substance as it exists in its natural state 

 Avithin an organism, where the colored prosthetic group is combined 

 or associated with a carrier which alters the physical or physiological 

 properties of the prosthetic group" (1). 



A long-time aim of research on plant pigments, especially on 

 chloroplast pigments, has been to determine the chemical state in 

 which the pigments exist naturally. Many attempts have been made 

 to isolate a pure form of nati\'e chlorophyll. Whether this has ever 

 been accomplished is questionable because it has never been demon- 

 strated that the preparations obtained act physiologically like 

 natural chlorophyll. Indeed, no easy and reliable physiological test 

 for isolated natural chlorophyll is available. This lack has hampered 

 progress toward the preparation of pure chlorophyll holochrome. 



* Postdoctoral Fellow of the United States Fnblie Health Service in the De- 

 partment of Chemistry, Stanford University, at the time when part of this work 

 was done. 



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