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<h1>Multiple Forms of Pectinesterase are Present in Tomato and Other Fruit</h1>
<h2>Introduction</h2>
<p>Pectinesterase (PE; EC 3.1.1.11) is an enzyme involved in the
degradation of plant cell walls. As well as its role in fruit ripening, PE often
interferes with the subsequent processing of fruit products. An understanding of its
action would, therefore, further basic research and bring commercial benefits to the food
industry.</p>
<p>Most work on PE has been conducted on tomato, in which <a href="PE_isoform.asp">at least 3 isoforms</a> have been identified. The dominant isoform (PE2) has
been purified, and the entire protein sequenced in order to determine its primary
structure. A cDNA clone corresponding to this isoform was isolated, and antisense
technology used to suppress PE2 gene expression. Fruit from these plants contained less
than 10% PE activity of normal fruit.</p>
<p>The residual PE activity in these plants was thought to be due to the activity of minor
isoforms with insufficient homology to PE2 for antisense downregulation to suppress their
gene expression. The downregulation of PE2 appeared to have little effect on the ripening
and processing characteristics of the fruit. Consequently, recent work has focused on the
minor isoforms, known as PE1 and PE3. Despite these being present in far smaller amounts
than PE2, their proteins have also been purified and sequenced. Additionally, unlike PE2,
these isoforms are not fruit specific, so could have other important roles in the plant.</p>
<p>Formerly, PE isoforms were separated using anion exchange on DEAE Sephadex A50. Our
method uses cation exchange on CM-Sepharose, which was reported by <a href="PE_references.asp">Warrilow et al. (1994)</a> to improve separation of the enzyme. Some work
has also been conducted using affinity chromatography on heparin, which was shown by <a href="PE_references.asp">Rillo et al. (1992)</a> to give excellent separation of PE.</p>
<p>Traditionally, a titrator had been used to measure PE activity. While satisfactory for
the calculation of total PE activity in fruit, it was obvious that the method would be
too time consuming for the analysis of column fractions, so a new technique was developed.
Our method uses a plate reader which can simultaneously read 96 samples, so is ideal for
the analysis of isoform profiles.</p>
<h2>Further Reading</h2>
<ul>
<li><a href="PE_default.asp">Title Page</a></li>
<li><a href="PE_introduction.asp">Introduction</a></li>
<li><a href="PE_assaydev.asp">Assay development</a></li>
<li><a href="PE_totalpe.asp">Total Pectinesterase activity in fruit</a></li>
<li><a href="PE_tomato.asp">Pectinesterase in Tomato</a></li>
<li><a href="PE_strawberry.asp">Pectinesterase in Strawberry</a></li>
<li><a href="PE_citrus.asp">Pectinesterase in citrus fruits</a></li>
<li><a href="PE_grape.asp">Pectinesterase in Grapes</a></li>
<li><a href="PE_summary.asp">Summary & Future work</a></li>
<li><a href="PE_references.asp">References</a></li>
</ul>
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