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The formation of UDP‐L‐rhamnose from UDP‐D‐glucose by an enzyme preparation of red campion ( Silene Dioica (L) clairv) leaves
Author(s) -
Kamsteeg John,
Brederode Jan Van,
Nigtevecht Gerrit Van
Publication year - 1978
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(78)81192-2
Subject(s) - population , biology , demography , sociology
In microorganisms at least three enzymes are involved in the conversion of TDP-D-glucose to TDP-Lrhamnose [I ,2]. The formation of TDP-4-keto-6deoxy-D-glucose, the first demonstrable intermediate, is catalyzed by TDP-D-glucose-4,6-hydrolyase (EC 4.2.1.43). This enzyme [3,4], which consists of two subunits firmly bound by one molecuie NAD’, initially attacks TDP-D-glucose at C-4 to yield TDP-4keto-D-glucose and enzyme-NADH. This TDP-4-ketoD-glucose then rearranges by &elimination of water between C-5 and C-6 to form an unsaturated glucoseen, which serves as hydrogen acceptor for the enzyme-NADH, and leads to the intermediate TDP-4keto-6-deoxy-D-glucose. Possibly via the ene-diol form, TDP+keto-6-deoxyD-glucose; 3,5-epimerase catalyzes the epimerizations at C-3 and C-S. The epimerizations are followed by a stereospecitic reduction by NADPH: TDP-6-deoxyL-lyxo4hexulose; 4-reductase. The 3,5-epimerase and 4-reductase are sometimes considered to be one single enzyme: TDP-L-rhamnose synthetase (see also fig.1) [S]. In plants the conversion of TDP-D-glucose to TDP-L-rhamnose proceeds with a very low efficiency ]6,7]. With UDP-D-glucose, however, the forlnation of UDP-L-rhamnose takes place at an appreciable higher rate [7]. It is not known whether in plants the synthesis proceeds according to the same reaction mechanism as in microorganisms. We here want to describe the conversion of UDP-Dglucose to UDP-L-rhamnose in Silene dioica and