Assay of human erythrocyte pyrimidine and deoxypyrimidine 5'-nucleotidase by isocratic reversed-phase high-performance liquid chromatography

Studies on erythrocyte pyrimidine 5'-nucleotidase (P5N) test and its evaluation in workers occupationally exposed to lead

An erythrocyte pyrimidine 5'-nucleotidase (P5N) test was performed for 171 workers occupationally exposed to lead. Erythrocyte P5N activity was markedly inhibited by exposure to lead. Among several biological indicators (erythrocyte P5N, delta-aminolevulinic acid dehydratase (ALAD), protoporphyrin (PROTO), urinary delta-aminolevulinic acid (ALA), coproporphyrin (COPRO)), the P5N activity had the highest correlation with the concentration of lead in blood (r = -0.77). A significant inhibition of erythrocyte P5N was found in groups of lead workers with blood-lead levels of more than 10 to 19 micrograms/dl. This P5N inhibition started before any changes occurred in urinary ALA and COPRO. A 45 to 50% inhibition of P5N corresponded to the blood-lead value (50 micrograms/dl) of the BEI recommended by ACGIH. In some lead workers, erythrocyte nucleotides (mainly CTP and UTP) were determined. The data indicated that a marked accumulation of these nucleotides had occurred, and their levels correlated negatively with P5N activity and positively with blood lead.

High-performance liquid chromatographic assay for thymidylate synthase from the human malaria parasite, Plasmodium falciparum

A rapid and highly sensitive high-performance liquid chromatographic assay for thymidylate synthase activity is described. The assay is based on the separation of the substrate, deoxyuridylate (dUMP), and its product, deoxythymidylate (dTMP), on a LiChrosorb RP-8 reversed-phase column with 44 mM triethylammonium phosphate (pH 7.0) as mobile phase and a flow-rate of 1.0 ml/min. In addition, using a mu Bondapak C18 reversed-phase column with 10 mM potassium phosphate (pH 4.0) and a gradient of 0-28% methanol, dUMP, dTMP and deoxythymidine (dTdR) are well separated within 30 min. The latter system is also applied to assay thymidine kinase activity with dTdR and dTMP as substrate and product, respectively. This method is sensitive enough to measure dTMP at concentrations as low as 25 pmol, and it was used to show that crude extracts of the human malaria parasite Plasmodium falciparum contain thymidylate synthase but not thymidine kinase activity.

Relationship between inhibition of erythrocyte pyrimidine 5'-nucleotidase activity and biological response for porphyrin metabolism in workers occupationally exposed to lead

A rapid determination of erythrocyte pyrimidine 5'-nucleotidase (P5N) activity in lead workers was carried out using a high-performance liquid chromatograph (HPLC). The P5N activity had a good negative correlation with the concentration of lead in blood (PbB) ranging from 16 to 96 micrograms/dl (r = -0.82, n = 77). Further, the P5N was compared with other biological parameters: erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity, erythrocyte protoporphyrin (PROTO), urinary delta-aminolevulinic acid (ALA) and urinary coproporphyrin (COPRO). The correlation coefficients between P5N and ALAD, log PROTO, log ALA, and log COPRO were 0.59, -0.72, -0.65, and -0.61, respectively. On the other hand, the normal value of P5N obtained from 72 healthy subjects was 11.9 +/- 2.1 units; mumol uridine/h/g Hb (mean +/- SD), indicating that the lower limit of 95% confidence interval for normal P5N was about 8 units. When P5N was cut off at less than or equal to 8 units in 77 lead workers, the validity (sensitivity + specificity) for PbB greater than or equal to 40 micrograms/dl, PbB greater than or equal to 60 micrograms/dl, erythrocyte PROTO greater than or equal to 150 micrograms/dl RBC, urinary ALA greater than or equal to 6 mg/l, and urinary COPRO greater than or equal to 150 micrograms/l was 1.66, 1.76, 1.57, 1.68, and 1.60, respectively. From these results, it was confirmed that the erythrocyte P5N test is suitable for the biological monitoring of exposure to lead in a wide range, and its activity is useful in predicting the disturbance of porphyrin metabolism induced by lead.

Erythrocyte pyrimidine 5'-nucleotidase and deoxynucleotidase isozymes: metallosensitivity and kinetics

Erythrocytes from a subject with classical pyrimidine 5'-nucleotidase (P5N) deficiency (PND) possessed typically low nucleotidase activity with uridine 5'-monophosphate (UMP) and cytidine 5'-monophosphate (CMP) as the substrates with subnormal dephosphorylation of 2'-deoxy thymidine 5'-monophosphate (dTMP) and 2'-deoxyuridine 5'-monophosphate (dUMP) and intermediate activity with 2'-deoxycytidine 5'-monophosphate (dCMP). Contrary to previously reported data, there was enzyme activity with all five substrates. The metallosensitivities of the P5N isozymes using UMP, dUMP, dCMP and dTMP as the substrates were defined. Nucleotidase (P5N) is slightly more sensitive than 2'-deoxy-pyrimidine 5'-nucleotidase (dP5N) to inhibition by lead, copper and mercury. Chromium stimulated more enzyme activity with dCMP than other substrates. Apparent Michaelis constants (Km) were calculated for UMP, CMP, dUMP, dCMP, and dTMP for PND and control subjects. Optimal activity was at pH 7.0-7.8 when using UMP and CMP as the substrates but at pH 5.5-6.5 with dUMP, dCMP and dTMP as the substrates. The Km, pH optima and metallosensitivities were, however, consistent with electrophoretic evidence for two and probably three isozymes: P5N with maximal affinity for UMP and CMP; dP5N with maximal affinity for dUMP and dTMP; and a closely related dCMPase. The relative activity with representative substrates can be used to distinguish homozygotes and heterozygotes for P5N deficiency and subjects with heavy metal exposure.

Red cell pyrimidine 5' nucleotidase deficiency: determination of nucleotidase activity and nucleotide content using HPLC

The hereditary deficiency of erythrocyte pyrimidine 5' nucleotidase has been investigated using an HPLC anion-exchange procedure designed to measure both red cell nucleotide content and enzymic activity. Red cell nucleotide profiles were determined using a low pH phosphate buffer salt-gradient system in 20 min, whereas a low pH buffer alone permitted the determination of enzymic activity with each of six different nucleotide substrates in less than 4 min. Both the red cell nucleotide profiles and the enzymic activity of haemolysates from two affected brothers and their children agreed well with previously published values. This unified approach should prove useful for detailed studies of deficiencies involving isoenzymes of pyrimidine nucleotidase.

High-performance liquid chromatographic profiling of nucleic acid components in physiological samples

The papers reviewed represent recent progress in HPLC profiling of nucleic acid components in physiological samples. Each method was designed for a particular application and possesses certain inherent advantages and/or disadvantages. Many methods are simply modifications of previous procedures. Although some methodologies appear to be superior to others, there is no "best" method for universal usage. The analyst must use the procedure which is best suited for the particular application at hand. This review is meant to be a starting point for the chromatographer who is comparing and evaluating HPLC methods for a given application.

Erythrocyte arginase, pyrimidine 5'-nucleotidase (P5N), and deoxypyrimidine 5'-nucleotidase (dP5N) as indices of lead exposure

The activities of three erythrocyte (rbc) enzymes, arginase, pyrimidine 5'-nucleotidase (P5N), and deoxypyrimidine 5'-nucleotidase (dP5N), were compared in 16 lead workers and 14 age matched controls as correlates of blood lead (PbB) and unextracted zinc protoporphyrin (EP) concentrations. Subjects with PbB of 0.9-2.5 microM (19-52 micrograms/dl) had 6.5 +/- 0.6 IU of P5N activity with uridine monophosphate (UMP) as substrate, significantly less (p less than 0.001) than the 12.0 +/- 0.7 IU activity of controls with PbB 0.3-0.6 microM (6-12 micrograms/dl). The mean activity of rbc dP5N with either deoxyuridine monophosphate (dUMP) or thymidine monophosphate as substrate, and of rbc arginase, did not differentiate the two groups. The correlation coefficients of ln PbB with the selected substrates for P5N and dP5N were: UMP, r = -0.75; dUMP, r = -0.61; TMP, r = -0.23. The correlation coefficient of ln PbB and arginase activity was -0.03. Rbc P5N (UMPase) is a significant correlate of PbB, equivalent to rbc protoporphyrin. HPLC assay of rbc UMPase activity is a sensitive and rapid assay that appears to meet criteria for a reliable clinical laboratory index of blood lead concentrations.