NMR spectroscopy studies of the action pattern of tomato pectinesterase: generation of block structure in pectin by a multiple-attack mechanism
✍ Scribed by Hans Grasdalen; Anne Kath Andersen; Bjørn Larsen
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 492 KB
- Volume
- 289
- Category
- Article
- ISSN
- 0008-6215
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✦ Synopsis
The enzymatic de-esterification of highly esterified poly(D-galacturonate) (degree of esterification, d.e. = 0.92, dpn --15) was monitored by 1H NMR spectroscopy. The enzymatic reaction resulted in a high content of homogeneous triads (GGG and EEE) demonstrating the production of a sequential structure. At high d,e. values, the enzymatic activity increased in proportion to the content of GE-diads. A multiple-attack mechanism was indicated by a relatively slow decrease of single G's (EGE) in the sequential structure. Production of EGG-triads in great preference to GGE-triads pointed to a degree of multiple-attack greater than the effective number average block length of E-residues, = 7-8, and, interestingly, the residue at the reducing end was de-esterified faster than that at the non-reducing end. These findings support the assumption that the enzyme attacks in alternating sequences (-GE-) and de-esterifies linearly preferentially towards the reducing end. Simulation-computed results are reported to demonstrate the difference between multiple-attack and multiple-chain mechanisms.