A high-pressure liquid chromatography procedure for monitoring nicotinate phosphoribosyltransferase activity

Determination of enzyme activity by high-performance liquid chromatography

The application of high-performance liquid chromatography (HPLC) in the study of enzymatic reactions is reviewed. The rationale for using HPLC is given and whether the components of the reaction mixture should be derivatized prior to or after HPLC. An alphabetical list of enzymes assayed by HPLC is given. Substrate and product are included as well the derivatization reagent, detection method and biological matrix. Specific examples of these assays in a complex biological matrix viz. faeces are given. Future prospects are the detection of new enzymes using synthetic substrates and implementation of mass spectrometry to elucidate enzyme specificities.

Enzymatic kinetic analyses that employ high-performance liquid chromatography. Competition between orotate- and hypoxanthine/guanine-phosphoribosyltransferases for a common substrate

Enzymatic assay procedures that employ high-performance liquid chromatography (HPLC) have been proven to be sensitive and versatile methods for accomplishing kinetic analyses of enzyme-catalyzed reactions, with nucleotides as substrates or products. Both orotate phosphoribosyltransferase (OPRTase) and hypoxanthine/guanine phosphoribosyltransferase (HGPRTase) have been purified from Baker's yeast and analyzed kinetically using a modification of published HPLC procedures. Because these two enzymes exist in the cytosol of yeast and might compete for the limiting (approximately equal to 15 microM) concentration of phosphoribosyl alpha-1-pyrophosphate (PRibPP), we elected to examine both equilibrium and steady-state effects of one enzymatic reaction on the other with HPLC. First, under the condition of equivalent mass concentrations of OPRTase and HGPRTase, the initial rate of orotidine monophosphate synthesis and the equilibrium state were greatly affected by the presence of HGPRTase activity. In contrast, the presence of the OPRTase activity had no effect on the HGPRTase-catalyzed reaction under these conditions. Second, to examine a competition by these enzymes for PRibPP in vivo, we have established that the total activities (units/ml) of OPRTase and HGPRTase in yeast cell extracts were 740 units/ml and 450 units/ml, respectively (a 1.7:1 ratio). These relative activities were then employed in an in vitro reaction competition analysis. The results were similar to the those obtained from experiments where equivalent OPRTase and HGPRTase activities were employed and reveal profound initial velocity and equilibrium effects of one reaction on the other. Thus a real competition between these enzymes for PRibPP may occur in the yeast cell cytosol, as determined by this unique HPLC competition assay procedure.

The pyridine-nucleotide cycle in tobacco : Enzyme activities for the recycling of NAD

In order to elucidate the NAD-recycling pathway the following enzyme activities have been characterized in different tobacco tissues and in tomato root: NAD pyrophosphatase, nicotinamide mononucleotide (NMN)/nicotinic acid mononucleotide (NaMN) glycohydrolases, nicotinamidase and nicotinic acid phosphoribosyltransferase. The investigations were performed with protein extracts purified by gel filtration and enzymatic activities were determined by high-performance liquid chromatography methods. The kinetic parameters of the different enzymes from tobacco root and their specificity are reported. The data are in favor of the so-called pyridine-nucleotide cycle VI (NAD→NMN→nicotinamide→nicotinic acid→NaMN→nicotinic acid adenine dinucleotide→NAD). In the nicotine-producing tobacco root a further direct route leading from NaMN to nicotinic acid is proposed. These data are reconciled with the assumption that it is nicotinic acid which is provided by the pyridine-nucleotide cycle for the synthesis of nicotine.

Enzymatic assay procedures that employ high-performance liquid chromatography: competition between phosphoribosyltransferases for a common substrate

A survey of the phosphoribosyltransferase (PRTase) activities in yeast has been accomplished using reversed-phase high-performance liquid chromatographic assay procedures. The following bases were observed to be utilized during phosphoribosyl pyrophosphate (PRibPP)-dependent nucleotide syntheses: adenine, xanthine, hypoxanthine, guanine, uracil, orotate, nicotinamide, nicotinate and quinolinate. Gradient elution procedures have also been perfected that allow the separation of the two following sets of PRTase assay components: (1) adenosine monophosphate, nicotinate mononucleotide, orotate, adenosine triphosphate, nicotinate, adenosine diphosphate, inosine monophosphate and hypoxanthine, and (2) nicotinate mononucleotide, nicotinamide mononucleotide, adenosine triphosphate, nicotinate, adenosine diphosphate and nicotinamide. Separation 1 has been employed to examine the PRibPP allocation among the hypoxanthine PRTase, orotate PRTase and nicotinate PRTase catalyzed reactions, whereas separation 2 has been employed to define the role that ATP plays in the nicotinamide PRTase-catalyzed reaction along with the allocation of nicotinamide between the reactions catalyzed by nicotinamide PRTase and nicotinamide deamidase.