Sucrose nucleoside diphosphate

Fig. 18. Substrate spectrum of sucrose synthase (EC 2.4.1.13) from rice grains in the cleavage reaction of sucrose (24) with nucleoside diphosphates [272,273]...

However, nucleoside diphosphates (NDP) are still expensive substrates, which can be obtained from much more cheaper nucleoside monophosphates (NMP). In this respect we have combined the SuSy-catalyzed cleavage of sucrose with the enzymatic formation of NDPs from NMPs catalyzed by nucleoside monophosphate kinase (NMPK, EC 2.7.4.4) or myokinase (MK, EC 2.7.4.3), including in situ regeneration of ATP with pyruvate kinase (PK, EC 2.7.1.40) (Fig. 20) [272]. Testing the substrate spectrum of four different kinases disclosed that none of them accepted dTMP as substrate [272], However, dUMP was well accepted by NMPK and dUDP-activated glucose could also substitute dTDP-activated glucose as precursor for the synthesis of activated deoxysugars (see below). The excellent enzyme stabilities under synthesis... 

Fig. 4 Synthesis of nucleotide sugars from sucrose and nucleoside diphosphates (NDPs) by a sucrose synthase...

Starting from sucrose, one-pot reactions are suitable to work as regeneration cycles for nucleotide sugars as demonstrated for UDP-Glc, UDP-Gal, and dTDP-deoxy-sugars [98-103] (Scheme 6.4). Sucrose synthase (SuSy), known for the reverse reaction of a GT, is used in combination with different enzyme module systems. Nucleoside diphosphate (NDP) from GT modules are substrates of SuSy catalyzed synthesis of activated glucose (UDP-Glc, dTDP-Glc) which enter enzyme modules to generate the donor substrates of GTs. 

An economically viable alternative to the synthesis of deoxyribonuclosides has been developed as a two stage process involving 2-deoxy-D-ribose 5-phosphate aldolase (DERA) (Fig. 6.5.14) (Tischer et al. 2001). The first step was the aldol addition of G3P to acetaldehyde catalyzed by DERA. G3P was generated in situ by a reverse action of EruA on L-fructose-1,6-diphosphate and triose phosphate isomerase which transformed the DHAP released into G3P. In a second stage, the action of pentose-phosphate mutase (PPM) and purine nucleoside phosphorylase (PNP), in the presence of adenine furnished the desired product. The released phosphate was consumed by sucrose phosphorylase (SP) that converts sucrose to fructose-1-phosphate, shifting the unfavorable equilibrium position of the later reaction. 

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