Biosynthesis pectin

The substrate for HGA synthesis is UDP-D-galacturonic acid (UDP-GalA) (81). UDP-GalA has been isolated from plants (59) and several pathways for its synthesis in planta have been reported (31). In vitro studies on pectin biosynthesis have been hampered since radiolabeled UDP-galacturonic acid is not commercially available. Previous researchers have used several... 

Cumming, C.M. and Brett, C.T. (1986) A galacturonyltransferase involved in pectin biosynthesis. In Cell Walls 86. Proceedings of the Fourth Cell Wall Meeting. Paris -September 10-12,1986. edited by B. Vian, et al, pp. 360-363. University Pierre et Marie Curie - Ecole Normale Superieure. Paris. 

Kauss, H. and Swanson, A.L. (1969) Cooperation of enzymes responsible for polymerization and methylation in pectin biosynthesis. ZJ aturforsch. 24 28-33. 

Key Words Plant cell-wall Pectin biosynthesis Methylester Golgi apparatus. 

Fifteen-day-old suspension cultures of Acer pseudoplatanus grown in Murashige and Skoog medium with 3% Glc, 4.4 pM 6-benzylaminopurine (BA) and 0.45 xM 2,4-dichlorophenoxyacetic acid (2,4-D) readily took up 100 mg/1 of [2-3H]MI over 24 h and utilized up to 20% for pectin biosynthesis. Virtually all of this 3H was recovered in galacturonosyl and pentosyl residues. Increasing the BA level 10-fold drastically blocked [2-3H]MI uptake and little was available for pectin biosynthesis. Increasing the 2,4-D level 10-fold had little or no effect on [2-3H]MI uptake but did diminish the amount of 3H appearing in pectin (Verma et al., 1976). 

Scheller H.V., Doong R.L., Rodley B.L., and Mohnen D. 1999. Pectin biosynthesis a solubilized a-l,4-galctouronosyl transferase from tobacco catalyzes the transfer of galacturonic acid from UDP-galacturonic acid onto the reducing end of homogalacturonan. Planta 207 512-517. 

A large number (>50) of glycosyltransferases and other types of transferase are required to synthesize pectic polysaccharides [20]. The activities of several glycosyltransferases have been identified in cell-free membrane preparations from plants. However, only a few of these enzymes have been partially characterized and shown to be involved in pectin biosynthesis. These include D-galacturonosyl transferase, galactosyl transferase, arabinosyl transferase, and apiosyl transferase [20]. An enzyme that catalyzes the methylesterification of homogalacturonan (homogalatur-onan methyltransferase) has been partially characterized [20]. There are also reports that plants contain methyltransferases that catalyze the methylesterification of RG-I and RG-II [25]. No 0-acetyl transferase involved in pectin biosynthesis has been characterized nor have the enzymes that catalyze the addition of phenolic acids to pectins [20]. 

This paper begins with a brief description of pectin structure and an overview of the general mechanism of cell wall polysaccharide biosynthesis. This is followed by a summary of previous research on PGA-GalAT and a description of a facile method to synthesize UDP-[ Cj-galacturonic acid. Finally, the paper ends with a summary of our work on the identificadon, partial characterization, and initial solubilization of the homogalacturonan biosynthetic enzyme PGA-GalAT. 

A full understanding of the role of pectin in plant development requires elucidation of the mechanisms that regulate p>ectin biosynthesis (6). Our strategy for studying the biosynthesis of HGA was to 1) establish a PGA-GalAT assay that would allow detection of synthesized HGA, 2) characterize the enzyme in microsomal membranes, 3) characterize the product synthesized by the enzyme in microsomal membranes, and 4) solubilize the enzyme and characterize the solubilized enzyme and its product. 

Kauss, H. (1974) Biosynthesis of pectin and hemicelluloses. In Plant Carbohydrate Biochemistry, edited by J.B. Pridham, pp. 191-205. Academic Press, London and New York. 

Kauss, H., Swanson, A.L., and Hassid, W.Z. (1967) Biosynthesis of the methyl ester groups of pectin by transmethylation from S-adenosyl-L-methionine. Biochem.BiophysJies.Commun. 26 234-240. 

ViUemez, C.L., Lin, T.-Y., and Hassid, W.Z. (1965) Biosynthesis of the polygalacturonic acid chain of pectin by a particulate enzyme preparation from phaseolus aureus seedlings. Proc.Natl.Acad.Sci.USA, 54 1626-1632. 

We observed that this activity is maximum five days after culture inoculation. Its biosynthesis is influenced by the glucose concentration. It is also stimulated hy pectin concentrations similar to the ones seen in fruit juices. 

During a study of the biosynthesis of pectin substances, a sensitive micromethod for the assay of pectinesterase activity was developed111 that uses a biosynthetically prepared [14C] methyl-labelled pectin as the substrate after enzymic de-esterification, the substrate remaining is precipitated with an excess of methanol and, after centrifugation, the [14C]methanol present in the supernatant liquor is counted in a liquid scintillation counter in order to assess the pectinesterase activity. 

Erlander, S. R. (1998a). Starch biosynthesis. I. The size distributions of amylose and amylo-pectin and their relationships to the biosynthesis of starch. Starch/Stdrke. 50,227-240. 

Ridley, B. L., O Neill, M. A., Mohnen, D. (2001). Pectins structure, biosynthesis, and oligogalacturonide-related signaling. Phytochemistry, 57, 929-961. 

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