Synopsis - Chlorophyll Biosynthesis and Technological Applications - page 46

2.10 Discovery of the Chlorophyll Biosynthetic
Heterogeneity

In 1970 an in vivo kinetic study of the biosynthetic relationship between Pchlide
(Fig. 2.7 , 3b) and its esterified analog, Pchlide ester, failed to demonstrate a
precursor-product relationship between these two protochlorophylls (Pchls)

(Rebeiz et al. 1970b ) as was commonly believed.
When the in vitro studies mentioned above failed to detect a direct precursor-
product relationship between these two Pchls (Fig. 2.7 ), we became suspicious that
the Chl biosynthetic pathway was more complex than proposed by Sam Granick.
Therefore we kept on the lookout for such evidence as we proceeded with our Chl
biosynthetic studies.

2.10.1 Discovery of Novel Tetrapyrrole Intermediates

After finishing the initial precursor-product studies mentioned above, we focused
our attention on studying the various Pchl-protein complexes, also known as Pchl-
holochromes (PchlHs) in various green plants. A postdoctoral trainee, by the name
of Charley Cohen, started working on the problem. Charley had just graduated from
Jerry Schiff's laboratory at Brandeis University. He started by looking at the
emission and excitation spectra at 77 K of PchlHs extracted from various green
plants grown under different conditions (Cohen and Rebeiz 1978 , 1981 ). During
one of our regular meetings I suggested to Charley that he should extract some of
the PchlHs with 80 % acetone and transfer the extracted pigments to ether in order
to establish standard 77 K emission and excitation fluorescence spectra in ether for
the purpose of adding this data to our tetrapyrrole database. That morning Charley
came running into my office and informed me that he was seeing strange looking
recorded spectra. I looked at the recorded 77 K Pchl spectra in ether and immedi-
ately realized that we were upon something exciting related to the suspected
putative Chl biosynthetic heterogeneity.
I asked Charley to continue his PchlH work and put a newly arrived Ph.D.
graduate student by the name of Faith Belanger on the Pchl extracts problem.

2.10.1.1 Discovery of the Ubiquitous Occurrence of Divinyl
Protochlorophyllide Occurrence in Higher Plants

In 1963, Jones reported that cultures of Rhodopseudomonas spheroides grown in the
presence of 8-hydroxyquinoline accumulated a novel Pchl that he identified as 2-4
divinyl Pchlide (DVPchlide) (Fig. 2.7 , 3a) (Jones 1963 ). He proposed that DVPchlide
was a transient intermediate in the formation of Chl that was rapidly converted to
conventional Pchlide (Fig. 2.7 , 3b) [i.e. Monovinyl Pchlide (MV-Pchlide)] by