Spinach phosphorylating enzyme

The natural acceptor aldehyde can be considerably varied among phosphorylated as well as unphosphorylated hydroxyaldehydes, which are both converted at comparable rates (Table 5)13-44 47. Although the catalytic reaction creates only a single stereocenter, the enzymes from yeast or spinach efficiently distinguish between adjacent configurations with preference for (3SAR)-i>yn isomeric ketose products44 47, which nicely parallel those derived from FruA reactions (Section 1.3.4.6.1). 

Transketolase from common yeast (Saccharomyces cerevisiae) is commercially available, but it is possible to work with a partially purified enzyme, isolated with little expense from spinach leaves.54 Transketolase catalyzes the transfer of a hydroxyacetyl group, reversibly from a ketose phosphate, or irreversibly from hydroxypyruvate to an acceptor aldose, phosphorylated or not.55 It requires thiamine pyrophosphate as a coenzyme, but only in catalytic amounts. In all the cases listed in Table V, the new chiral center, C-3 of the ketose, has the l-glycero configuration. 

Vanadate-induced photo-oxidation of serine and subsequent cleavage of the protein were also observed for ribulose-l,5-diphoshate carboxylase/oxygenase from spinach leaves. Activity could be restored by treatment with sodium boronate, which reduces formylglycine back to serine.Similarly, vanadate-induced UV oxidation of threonine (Thr353, at the phosphorylation site) in the sarcoplasmatic reticulum (SR) Ca +-ATPase can be restored by reduction with Na[BH4]. For monovanadate to become catalyti-cally active it is essential that Mg + and ADP bind to the phosphorylation site of the enzyme in its Ca +-receptive conformation, suggesting the formation of an active MgADPV as proposed for the myosin fragmentation. In contrast, decavanadate catalyses the photo-oxidation of a serine (Seri 86) residue in the SR ATPase in the absence of ADP.P bl... 

Phosphorylating (P) Enzyme. The formation of ATP associated with cleavage of succinyl CoA is catalyzed by the P enzyme. This enzyme has been purified from both heart muscle and spinach. In both cases a single protein appears to carry out the reaction ... 

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