Differential phosphorylation of azidothymidine, dideoxycytidine, and dideoxyinosine in resting and activated peripheral blood mononuclear cells.

The antiviral activity of azidothymidine (AZT), dideoxycytidine (ddC), and dideoxyinosine (ddI) against HIV-1 was comparatively evaluated in PHA-stimulated PBM. The mean drug concentration which yielded 50% p24 Gag negative cultures were substantially different: 0.06, 0.2, and 6 microM for AZT, ddC, and ddI, respectively. We found that AZT was preferentially phosphorylated to its triphosphate (TP) form in PHA-PBM rather than unstimulated, resting PBM (R-PBM), producing 10- to 17-fold higher ratios of AZTTP/dTTP in PHA-PBM than in R-PBM. The phosphorylation of ddC and ddI to their TP forms was, however, much less efficient in PHA-PBM, resulting in approximately 5-fold and approximately 15-fold lower ratios of ddCTP/dCTP and ddATP/dATP, respectively, in PHA-PBM than in R-PBM. The comparative order of PHA-induced increase in cellular enzyme activities examined was: thymidine kinase > uridine kinase > deoxycytidine kinase > adenosine kinase > 5'-nucleotidase. We conclude that AZT, ddC, and ddI exert disproportionate antiviral effects depending on the activation state of the target cells, i.e., ddI and ddC exert antiviral activity more favorably in resting cells than in activated cells, while AZT preferentially protects activated cells against HIV infection. Considering that HIV-1 proviral DNA synthesis in resting lymphocytes is reportedly initiated at levels comparable with those of activated lymphocytes, the current data should have practical relevance in the design of anti-HIV chemotherapy, particularly combination chemotherapy.

The role of the transferrin receptor in lymphocyte activation.

Blockade of the transferrin receptors whose expression is induced in lymphocytes incubated with the mitogenic lectin phytohaemagglutinin (PHA) does not affect the initial stimulation of protein synthesis but does strongly and progressively inhibit the subsequent induction of DNA synthesis. When the effects of transferrin receptor blockade on the induction of the enzymes uridine kinase (whose induction begins early in G1 phase of the cell cycle) and thymidine kinase (whose induction is closely associated with DNA synthesis) were examined, both enzymes were found to be induced normally. This indicates that the function of the transferrin receptor is directly to provide a component essential for DNA synthesis itself (probably iron) rather than to act as the receptor for a general signal required to initiate entry into S-phase.

[Coordination of the main and reutilization pathways of nucleotide biosynthesis in the lymphocytes in leukemia]. / Koordinatsiia osnovnogo i reutilizatsionnogo putei biosinteza nukleotidov v limfotsitakh pri leikoze.

Coordination of these two pathways of nucleotide synthesis in leukocytes under chronic lympholeukosis was studied using incorporation of 14C-orotic acid and 14C-uridine into uridine mono-, di- and triphosphates and also into RNA. Simultaneously, activity of the key enzymes, participating in metabolism of orotic acid and of uridine, was measured: OMP-pyrophosphorylase /EC 2.4.2.10, orotidine-5'-phosphate: purophosphate phosphorybosyl transferase/ and uridine kinase /EC 2.7.1.48, ATP: uridine-5'-phosphotransferase/. The reutilizational pathway of pyrimidine nucleotide synthesis was distinctly activated. At the same time there was only a slight increase in the main pathway of their synthesis in lymphocytes in leukemic form of cronic lympholeukosis. Activities of OMP-pyrophosphorylase and uridine kinase were increased by 30%. An impairment in the coordination of the rates of both pathways of pyrimidine nucleotide synthesis was related to inhibition of OMP-pyrophosphorylase caused by and increase in uridine nucleotide pool.

Red cell uridine monophosphate kinase: effects of red cell aging on the activity of two UMPK gene products.

We have previously reported that uridine monophosphate kinase (UMPK) is genetically polymorphic in man, and that the UMPK2 gene product has less activity than that of UMPK1 when measured in normal red cells. In this paper we present evidence that the activity of UMPK, like that of many other enzymes, declines during red cell aging, and that the lower activity of UMPK 2, as compared with UMPK 1, is best explained by its more rapid catabolism.

Red cell uridine monophosphate kinase polymorphism in Japanese.

Samples from 635 unrelated Japanese blood doners in Tokyo were examined for their red cell uridine monophosphate kinase phenotypes using starch gel electrophoresis. Three phenotypes were found: UMPK1 (570, 89.76%), UMPK 2--1 (63, 9.92%) and UMPK 2 (2, 0.32%). The corresponding gene frequency for UMPK1 was 0.9472 and for UMPK2 was 0.0528. The UMPK2 frequency in the present study was slightly higher than the previously reported value for Caucasians in the United States, but the difference is not statistically significant. A study of 15 twin pairs and their parents was in agreement with the hypothesis of autosomal codominant inheritance for UMPK.

Red-cell uridine-5-monophosphate kinase (UMPK): formal genetics, linkage analysis and population genetics from southwestern Germany.

In a population sample from southwestern Germany the frequency of UMPK1 was estimated to be 0.949. The segregation of the children's phenotypes is in agreement with the formal model: 2 common alleles UMPK1 and UMPK2 at an autosomal locus. Data on linkage relations are referred.

Polymorphism of red cell enzymes in Alaskan ethnic groups.

1. Gene frequencies of esterase D, glyoxalase I and uridine monophosphate kinase in Alaskan populations were determined. 2. Improved methods for demonstrating phenotypes of glyoxalase I and uridine monophosphate kinase are presented. 3. Rare variants of adenylate kinase (AK1) and diaphorase (DIA) were found. One of the AK1 variants is new. 4. Gene frequencies were notably diverse within major ethnic groups. This variability was consistent with a population structure composed of small groups that were relatively isolated from one another.

Deoxycytidine kinase: properties of the enzyme from human leukemic granulocytes.

Deoxycytidine kinase, which phosphorylates deoxycytidine (CdR) and its analog, cytosine arabinoside (ara-C), has been purified 71-fold from human leukemic cells. Biochemical properties of the partially purified enzyme included a molecular weight of 68,000, Kms of 7.8 muM for CdR and 25.6 muM for ara-C, and optimal activity with ATP and GTP as phosphate donors. Ara-C phosphorylation was strongly inhibited by CdR (Ki = 0.17 muM) and dCTP (Ki = 7.3 muM) and was weakly inhibited by ara-CTP (Ki = 0.13 mM). Purification by calcium phosphate gel elution and DEAE chromatography effectively separated this enzyme from cytidine deaminase, which deaminates both CdR and ara-C, and from uridine-cytidine kinase, the enzyme which phosphorylates 5-azacytidine. CdR kinase activity was found to decrease and cytidine deaminase to increase with maturation of normal and leukemic granulocytes. Myeloblasts purified by Ficoll sedimentation revealed an average kinase activity of 15.4 U/mg protein in acute myelocytic leukemia and 12.3 U/mg protein in blastic crisis of chronic myelocytic leukemia (CML). The average ratio of CdR kinase to deaminase activity in crude cell extracts varied from 0.197 in AML and 0.089 in blastic crisis to 0.0004 in normal granulocytes, reflecting the changes which take place with cellular maturation. The absolute levels of kinase and deaminase and the ratio of these two enzymes varied considerably among patients with AML, indicating that quantitative differences may be found in the metabolism of CdR and its analogs in leukemic cells.