Functional nonequivalence of transketolase active centers

Abstract

SummaryTransketolase (TK, EC 2.2.1.1), the key enzyme of the nonoxidative branch of pentose phosphate pathway of hydrocarbon transformation, plays an important role in a system of substrate rearrangement between pentose shunt and glycolysis, acting as a reversible link between the two metabolic pathways. In addition, it supplies precursors for biosyntheses of nucleotides, aromatic amino acids, and vitamins. In plants, the enzyme plays a central role in the Calvin cycle. TK catalyzes interconversion of sugar phosphates. Thiamine diphosphate (TDP) and bivalent cations serve as its cofactors. Being a typical TDP-dependent enzyme, TK is the least complex representative of this group of enzymes, and this accounts for its use as a model in studies of their structure and mechanism of action. TK is readily crystallized, this being the reason why the first crystal X-ray structure analysis of TDP-dependent enzymes was performed with a TK sample. Both the general structure of TK and the structures of its active centers have been studied in detail. In this article, we review experimental evidence of functional nonequivalence of the two active centers of TK, which are known to be identical by crystal X-ray structure analysis. half-of-the-sites reactivity.Abbreviations TK, Transketolase; TDP, thiamine diphosphate; X5P, xylulose 5-phosphate; R5P, ribose 5-phosphate; F6P, fructose 6-phosphate; DHETDP, dihydroxyethylthiamine diphosphate.

C−C Bond-Forming Lyases in Organic Synthesis

“…Transketolase (TK, EC 2.2.1.1) catalyzes the reversible transfer of a hydroxyacetyl group among a number of phosphorylated sugars, using thiamine diphosphate (ThDP) and Mg 2+ (or Ca 2+ ) as cofactors. ,,− The enzyme is a transferase with homodimeric structure, molecular weight of 74 kD, and two active sites located at the interface between the contacting monomers . Its role in nature, as a key enzyme in the pentose-phosphate pathway, is the transfer of a 2-C hydroxyacetyl fragment from a ketose-phosphate ( d -xylulose-5-phosphate, D -X5P) to an aldose phosphate ( d -ribose-5-phosphate, d -R5P), thus generating d -sedoheptulose-7-phosphate and G3P (Figure ).…”

“…TK from E. coli was also cloned and overexpressed in recombinant E. coli strains, and it is easily available for preparative scale reactions. − The first thiamine diphosphate-dependent enzyme for which the three-dimensional structure was determined was TK from S. cerevisiae , ,, followed by TK from E. coli . Later on, crystal structures of the key intermediates in thiamine catalysis showing ThDP bound at the active site of the enzyme were determined as well. ,,, …”

Accumulation of functional metabolites and transcriptomics in postharvest fume‐drying and air‐drying process in rhubarb

“…Glucose‐6‐phosphate dehydrogenase (G6PD) serves as a critical enzyme in PPP and remarkably affects the oxidative stress reaction by generating NADPH, the primary endocellular reducing agent 41 . Transketolase (tktA) is a critical enzyme in the non‐oxidation group of the PPP and is involved in hydrocarbon transformation 42 . In our study, G6PD and tktA were up‐regulated in FD versus FR and AD versus FR and down‐regulated in FD versus AD.…”

Using gene networks to identify genes and pathways involved in milk production traits in Polish Holstein dairy cattle

“…The pathway includes transketolases (TK), which play an important role in the system of substrate rearrangement between pentose shunt and glycolysis, permitting the cell to adapt to a variety of metabolic conditions (Sax et al 1996). Its presence is necessary for the production of NADPH, especially in tissues actively engaged in biosyntheses, such as mammary glands (Kochetov and Sevostyanova 2010). In the case of a link between protein yield and the endocytosis pathway (bta04144) it is known that endocytic mechanisms serve many important cellular functions, including the uptake of extracellular nutrients, regulation of cell-surface receptor expression, maintenance of cell polarity, and antigen presentation (Mukherjee et al 1997;Clague 1998).…”