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<h1 class="top">Structure of glycogen</h1>
<p class="header">This page discusses the structure of glycogen and
is one of a series that discuss
common errors in current textbooks of biochemistry.</p>
<p class="shout"><br>All of the pages in this series are in <strong>urgent need of updating.</strong>
The biochemical principles have not changed, of course, but textbooks have: some of
those that were current when I first prepared these pages in 2000 have appeared in new editions, and
others have ceased to be widely used. New books have appeared that are not discussed. Unfortunately
I do not have easy access to any of the commonly used textbooks, as I work in a research (not teaching)
environment in a country where English is not the everyday working language. I could buy them, of course,
but that would represent rather a large investment for the sake of a few web pages.<br><br>Accordingly
I should be grateful if someone would collaborate with me in the revision. If you have access to
all of the textbooks published in English in the past ten years (say 1996 or later)
that are commonly used for teaching biochemistry, and if you would like to
help, please contact me at acornish@ibsm.cnrs-mrs.fr.
<h2 class="framed">The actual structure</h2>
<div class="sidebar-medium">
<p class="in-sidebar"><strong>Other errors</strong><br>
<p class="in-sidebar"><a href="stereo0.htm">Stereochemical prefixes</a>
<p class="in-sidebar"><a href="liverhk0.htm">Liver hexokinase</a>
<p class="in-sidebar"><a href="asympt.htm">Michaelis–Menten kinetics</a>
<p class="in-sidebar"><a href="effic0.htm">Metabolic <q>efficiency</q></a>
<p class="in-sidebar"><a href="zwitter.htm">Uncharged amino acids</a>
<p class="in-sidebar"><a href="rls0.htm">Control of glycolysis</a>
<p class="in-sidebar"><a href="choles.htm">Plant cholesterol</a>
</div>
<p>The structure of glycogen is essentially as shown in the following
drawing, except that in the complete glycogen molecule there are 12 layers whereas for simplicity only 5 are shown in the drawing:
<div class="centred">
<h4><img src="images/glycogen.gif" width="225" height="209" alt=" [Structure of glycogen] ">
</h4></div>
<p>This is taken from Fig. 1d of <a href="#enrref">Meléndez-Hevia</a>
<cite>et al.</cite> (2000), who comment that
<p class="quotation">The essential features of this general structure are that each B-chain has two branch points, and all chains
have the same length, as the experiments showed that the material is distributed at 50% between A- and B-chains.
</p>
<p>In addition it is worth noting the molecule of glycogenin, a protein that acts as a primer, at the centre of the structure.
<p>Despite the fact that this structure was worked out by <a href="#gunjaref">Whelan’s group</a> nearly thirty years ago, and is accepted by all workers
in the glycogen field, i.e. there is no current controversy about it
(see, for example, the review by <a href="#calder">Calder),</a>
virtually all textbooks show the completely obsolete structure
suggested by Meyer and Bernfeld in 1940, and do not mention the protein component. This structure is distinguishable from
the correct structure by a more haphazard appearance, without a clear distinction between A and B chains, with variable chain lengths and
with more than or less than two branch points per B-chain. In addition, of course, the glycogenin molecule at the core is omitted, as
this was not suspected in 1940.
<h2 class="framed">What the textbooks say</h2>
<p>All of the textbooks examined either give the incorrect structure or show the structure
so vaguely that it is difficult to guess whether it is based on the correct one or not. If they mention
glycogenin at all they do so in a different context from the one in which the structure is given. The
only textbook that I know of (see <a href="#murray">below)</a> that presents the information correctly was not among
those considered in relation to the other errors discussed.
<p>Despite showing the obsolete structure, <a href="howler.htm#campbell">Campbell</a>
refers in her text (pp. 419–420) to some of the results from modelling
the structure (results that refer, however, to the real structure, not the one she shows):
<p class="quotation">
It has been shown by mathematical modeling that the structure of glycogen is
<em>optimized</em> for its ability to store and deliver energy quickly and for the longest amount of time possible.
The key to this optimization is the average length of the branches (13 residues). If the average chain length were
much greater or much shorter, glycogen would not be as efficient a vehicle for energy storage and release on
demand. Experimental results support the conclusions reached from the mathematical modeling.
</p>
<p>According to <a href="howler.htm#stryer">Stryer</a> (p. 587),
<p class="quotation">
Elongation stops when the synthase is no longer in contact with glycogenin, which forms the core of the
particle. <i>The synthase-glycogenin interaction limits the size of glycogen granules.</i> We see here a simple
and elegant molecular device for setting the size of a biological structure.
</p>
<p>However, this <q>simple and elegant molecular device</q> appears to be pure fantasy. It is not explained how
a small 38 <acronym class="deja" title="kilodalton">kDa</acronym> protein buried deep inside a 1000 <acronym class="deja" title="kilodalton">kDa</acronym> polymer can remain in contact with an enzyme working on the surface.
<p><a name="murray"></a>I thank Enrique Meléndez-Hevia for informing me that the correct structure is shown
in the chapter by R. K. Murray, D. K. Granner, P. A. Mayes & V. W. Rodwell in
<cite>Harper’s Biochemistry</cite> (24th edn., Prentice-Hall International, London, 1996, p. 143).
As this book was not among those I had easy access to when making the original survey it
is not at present included in these pages. However, I shall try to include it when I have
more information about the other questions considered.
<h2 class="framed">Textbook checklist</h2>
<div class="table">
<table>
<tr>
<td valign="top"><a href="howler.htm#abeles">Abeles, Frey and Jencks</a></td>
<td valign="top"><img src="images/yellowba.gif" alt="Poor" width="14" height="14" title="Partially incorrect"></td>
<td valign="top">Structure of whole molecule not indicated; no glycogenin</td>
<td valign="top">p. 435–437</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#campbell">Campbell</a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Meyer and Bernfeld (1940) structure; no glycogenin</td>
<td valign="top">pp. 419–420</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#garrett">Garrett and Grisham</a></td>
<td valign="top"><img src="images/yellowba.gif" alt="Poor" width="14" height="14" title="Partially incorrect"></td>
<td valign="top">Structure of whole molecule not indicated; no glycogenin</td>
<td valign="top">p. 678</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#horton">Horton <cite>et al.</cite></a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Meyer and Bernfeld (1940) structure; glycogenin mentioned later (p. 385)</td>
<td valign="top">p. 232</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#lehninger">Lehninger, Nelson and Cox</a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Meyer and Bernfeld (1940) structure; glycogenin mentioned later (p. 614)</td>
<td valign="top">p. 309</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#mckee">McKee and McKee</a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Meyer and Bernfeld (1940) structure; glycogenin mentioned later (p. 183)</td>
<td valign="top">p. 168</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#mathews">Mathews, van Holde and Ahern</a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Meyer and Bernfeld (1940) structure; glycogenin mentioned later (p. 573)</td>
<td valign="top">p. 472</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#stryer">Stryer</a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Unclear, but appears to be Meyer and Bernfeld (1940) structure; glycogenin assigned
a fantastic function</td>
<td valign="top">p. 19</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#voet">Voet and Voet</a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Meyer and Bernfeld (1940) structure; glycogenin mentioned later (p. 492)</td>
<td valign="top">p. 485</td>
</tr>
<tr>
<td valign="top"><a href="howler.htm#zubay">Zubay</a></td>
<td valign="top"><img src="images/redball.gif" alt="Bad" width="14" height="14" title="Major error"></td>
<td valign="top">Meyer and Bernfeld (1940) structure; no glycogenin</td>
<td valign="top">p. 9</td>
</tr>
</table></div>
<h2 class="framed">References</h2>
<p><a name="calder"></a> P. C. Calder
(1991) <q>Glycogen structure and biogenesis</q>
<cite><acronym class="deja" title="International Journal of Biochemistry">Int. J. Biochem.</acronym></cite> <strong>23,</strong> 1335-1352
<p><a name="gunjaref"></a> Z. Gunja-Smith, J. J. Marshall, C. Mercier, E. E. Smith and W. J. Whelan
(1971) A revision of the Meyer–Bernfeld model of glycogen and amylopectin,
<cite><acronym class="deja" title="FEBS (Federation of European Biochemical Societies) Letters">FEBS Lett.</acronym></cite> <strong>12,</strong> 101–104
<p><a name="enrref"></a>E. Meléndez-Hevia, R. Meléndez
and E. I. Canela (2000) <q>Glycogen Structure: an Evolutionary View</q>, pp. 319–326 in
<a href="buchner.htm"><cite>Technological and Medical Implications of Metabolic Control Analysis</cite></a>
(ed. A. Cornish-Bowden and M. L. Cárdenas), Kluwer Academic Publishers, Dordrecht
<hr>
<p><a href="howler.htm">Other common errors in textbooks</a>
<p><a href="howler.htm#boox">List of books considered</a>
<hr>
<div class="sidebar-tail">
<p class="in-tail">
Page created on 18 April 2000<br>
Last update: 22 December 2008<br>
Last significant update: 14 October 2005<br>
Comments and corrections to this page are welcome, and may be sent to <a href="mailto:acornish@ibsm.cnrs-mrs.fr">Athel Cornish-Bowden</a><br>
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