Development of Cell-Free Systems - Chlorophyll Biosynthesis and Technological Applications - page 130

Chapter 4
Development of Cell-Free Systems
All truths are easy to understand once they are discovered.
The point is to discover them (Galileo Galilei).
4.1 Prologue
Originally, work on the biosynthesis of protochlorophyll(ide) [Pchl(ide)] and chloro-
phyll (Chl) in organello, started in 1967 in my laboratory at the National Research
Institute in Tel-el-Amara, Lebanon (see Chap. 2 )(Rebeiz 1967 , 1968 ). At the time
spectrophotometric instrumentation was used. Since I was aware that excised etiolated
cucumber cotyledons greened very rapidly, within hours, in the light, I conjectured
that if greening cotyledons were homogenized, I should be able to observe Pchl(ide)
and Chl formation in the homogenate for a few minutes before the system fell apart.
The first evidence of Chl biosynthesis in organello was observed in 1967 (Rebeiz
1967 ). However I soon realized that spectrophotometric techniques were not sensitive
enough to observe consistent and reliable Pchl(ide) and Chl biosynthesis in organello.
I therefore shifted to the use of 14 C- δ -aminolevulinic acid ( 14 C-ALA) as a precursor of
14 C-Chl. At the time ALA was known as a tetrapyrrole precursor (Granick 1961 ). We
observed the first incorporation of 14 C-ALA into 14 C-Chl in my laboratory in 1969.
The work was perfected in California at UC Davis in 1969-1970 when I joined Paul's
Castelfranco Laboratory (Rebeiz and Castelfranco 1971a , b ).
After 10 years of research the developed in organello and cell-free systems of
Pchl(ide) and Chl biosynthesis were finally perfected in my laboratory at the
University of Illinois, in Urbana-Champaign and the systematic investigations of
the chlorophyll biosynthetic pathway became a possibility. An account of the
gradual perfection of these systems will be described in this chapter.