Substrate glycerol kinase

Glycerol kinase uses a simple carbohydrate, glycerol, as its substrate converting it to optically pure sn-glyoerol-3-phosphate (R = OH) (see Chapter 6). The enzyme shows a broad substrate tolerance and has been used to phosphorylate a range of glycerol analogues (33) as shown in Scheme 5.28. 

Enantioselective Phosphorylation. Glycerol kinase [544] is not only able to accept its natural substrate, glycerol, to form sn-glycerol-3-phosphate [545], or close analogs of it such as dihydroxyacetone (see Scheme 2.83), but it is also able to transform a large variety of prochiral or racemic primary alcohols into chiral phosphates (Scheme 2.85) [546-548]. The latter compounds represent synthetic precursors to phospholipids [549] and their analogs [550],... 

The evaluation of the data obtained fi om more than 50 substrates permitted the construction of a general model of a substrate that would be accepted by glycerol kinase (Fig. 2.14). 

The analysis of DL-glycerol-3-phosphate disodium hexahydrate (33) was carried out to provide geometrical details for correlation with structural studies of enzymes, the D-isomer being an inhibitor of triose phosphate isomerase (TIM), whereas the L-isomer is both a substrate and inhibitor for glycerol kinase. The most intmesting feature of the molecular geometry is... 

Figure 27.10 A double-reciprocal plot for the initial phosphorylation rate v of glycerol kinase against the concentration of the substrate aminopropanediol, at various concentrations of MgATP. (o) 0.126mM ( ) 0.504 mM ( ) 2.52 mM. Source J Kyte, Mechanism in Protein Chemistry, Garland, New York, 1995. Adapted from WB Knight and WW Cleland, Biochemistry 28, 5728 (1989).

Several luminescent systems have been described, one of the more commonly used being the firefly luciferase system. This uses ATP as one of its substrates and light is emitted during the course of the chemical reaction. The enzyme can therefore be used in reactions where ATP is formed or consumed, e.g. creatine kinase assay, or the measurement of glycerol by glycerol kinase. Luminescent immunoassays, analogous to radioimmunoassay or enzyme-immunoassay have also been described, using luminol or luminol derivatives as the label. 

Crans DC, Whitesides GM. Glycerol kinase substrate specificity. J. Am. Chem. Soc. 1985 107 7008-7018. 

Hayaishi and colleagues, who devised the purification for the Brevibacter-ium liquefaciens enzyme, used it to characterize the reversibility of the adenylate cyclase reaction (Kurashina et ai, 1974) and found that the equilibrium constant for the reaction written in the direction of cyclic AMP formation is 0.12 Mat pH 7.3 at this pH the rates of the forward and reverse reactions are comparable but about the rate of the forward reaction measured at its pH optimum, pH 9. Our plan for determining the stereochemical course of the reaction is shown in Fig. 14. Since we had synthesized the diastereomers of cyclic [, 0]dAMP, we would use the cyclase to catalyze their pyrophosphorolysis and form the diastereomers of [a- 0, 0]dATP. However, the thermodynamics of the cyclase reaction prevents an efficient conversion of cyclic dAMP to dATP, so this reaction was coupled to the glycerol kinase reaction the kinase reaction utilizes the thermodynamic instability of the )J,y-anhydride bond to displace the overall equilibrium to favor the synthesis of the diastereomers of [a- 0, 0]dADP. Both the cyclase and glycerol kinase can utilize deoxyadenosine nucleotides as substrates, but only the cyclase reaction can alter the configuration of the chiral phosphorus atoms. 

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