In article <01I2HXMT2G5I8Y7PI3 at VAX1.JMU.EDU>, MONROEJD at jmu.edu (Jon
Monroe) wrote:
> Sam: Can you tell us why the pheophytin spot on silica gel TLC (Reiss 1994)
> appears to be only a single spot and not two? Is one of the chlorophylls more
> sensitive to degradation, or is what we see the normal level of pheophytin
> in extracts (either a or be but not both)? Since chl a and b separate so well
> I would assume the respective pheophytins would also.
Well, Reiss informs me that her students often do get both pheophytins on
their TLC plates. The two pheophytins do separate at least as well as the
two chlorophylls on silica gel TLC. Keep in mind that there is usually
much less chlorophyll b than chlorophyll a in plant extracts, and that the
light absorption of pheophytin b is less than that of pheophytin a, so
these two things conspire to make visual detection of phrophytin b
difficult. But, it's true that chlorophyll a is more susceptable to loss
of Mg under mild acidic conditions than is chlorophyll b. In fact, this
difference was used as the basis for a novel analytical method
(Laval-Martin, D. (1985) Spectrophotometric method of controlled
pheophytinization for the determination of both chlorophylls and
pheophytins in plant extracts. Anal. Biochem. 149, 121-129).
