Extraction of protein and starch from plants

Gary Cote gcote at runet.edu
Fri Jan 7 09:36:17 EST 2000

Hi all,

I do a lab in which students choose a biological material of interest to
them and then extract carbohydrate, lipid, protein and nucleic acid.  This
procedure is one I adapted from another professor who used it to extract
from yeast.  I warn the students that the procedure may not work for them,
and part of the pedagogy of the lab is figuring out why they didn't get the
results they expected (not always because it didn't work --one student was
amazed to find proteins in a plant!)

They start by precipitating most everything with TCA.  They then prepare
glycogen/starch from the supe, and isolate nucleic acid from the pellet by
NaCl extraction.  Following this they extract protein and lipid from the
remaining precipitate by a standard Folch.  Carbohydrates are detected by
Benedict's test following amylase digestion, and by the iodine test for
starch.  Nucleic acids are detected by spectroscopy, proteins by PAGE, and
lipids by TLC.

It would be nice if it did work better than it does, however.  This past
semester students obtained no or very little protein from green plant
material, or from carrot root.  Abundant proteins were found only in animal
tissues, apple seeds, and potato tuber.  It's possible some had good
protein pellets, but never got them into the PAGE buffer.

Nobody obtained carbohydrate from anything--much to the puzzlement of
students using carrot root or liver.

Lipids worked well, and the students had a challenge figuring out what the
green one was.  ("But chlorophyll is a pigment, not a lipid!!!")

Anyway, can anyone suggest ways to improve protein extraction from plant
material.  Similarly can anyone suggest good procedures to extract
starch/glycogen from anything.

If anyone is interested I'll be glad to discuss the lab in more detail
privately or publicly.


Dr. Gary Coté
Assistant Professor
Department of Biology
Box 6931
Radford University
Radford, VA 24142-6931

Ph: 540-831-5630
Fax: 540-831-6615
email: gcote at runet.edu

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