Glucosinolates are a diverse group of molecules found in plants of the order
Capparales and the genus Drypetes. Hydrolysis of glucosinolates is catalysed by a
thioglucosidase, myrosinase. Myrosinase has not only been detected in almost all
glucosinolate-containing plants but also in insect and microbial species.
Phylogenetic analysis of glucosinolate-containing plants found that all were
clustered together with the exception of the outlier genus Drypetes. The important
question is whether myrosinase in Drypetes arose from the same ancestral gene as
that in the Capparales, or whether it arose from a different source. Myrosinaselike
activity was detected in D. natalensis. A candidate molecule for the observed
activity was isolated and found to be a 50 kDa heterodimer with subunits of
approximately 30 kDa and 20 kDa. This contrasts with Capparales myrosinases
which are typically 130-150 kDa homodimers. A 1047 bp partial sequence
corresponding to the larger subunit was obtained. Analysis of the nucleic acid and
amino acid sequence showed that it was similar to the cupin superfamily of
proteins which include the ubiquitous seed storage proteins. Phylogenetic analysis
showed that the isolated protein was closely related to seed storage proteins. The
results obtained here are suggestive of an independent origin of myrosinase
activity in Drypetes. With the degree of functional plasticity observed in the cupin
superfamily it is proposed that the isolated factor could have acquired myrosinaselike
activity. However, purification and further characterisation of the enzyme
responsible for the observed activity is still required to confirm the results
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/14887 |
| Date | 07 July 2014 |
| Creators | Letseka, Ntutu |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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