Mitochondrial ATP synthase: dramatic Mg2+-induced alterations in the structure and function of the F1-ATPase moiety

The ATPase activity of the F1 moiety of rat liver ATP synthase is inactivated when incubated prior to assay at 25 degrees C in the presence of MgCl2. The concentration of MgCl2 (130 microM) required to induce half-maximal inactivation is over 30 times higher than the apparent Km (MgCl2) during catalysis. Moreover, the relative efficacy of divalent cations in inducing inactivation during prior incubation follows an order significantly different from that promoting catalysis. Inactivation of F1-ATPase activity by Mg2+ is accompanied by the dramatic dissociation from the F1 complex of alpha subunits and part of the gamma-subunit population. The latter form a precipitate while the beta, delta, and epsilon subunits, and the remaining part of the gamma-subunit population, remain soluble. Dissociation is not a sudden "all or none" event but parallels loss of ATPase activity until alpha subunits have almost completely dissociated together with about 50% of the gamma-subunit population. Mg2+-induced loss of F1-ATPase activity cannot be prevented by including either the hydrolytic substrates ATP, GTP, or ITP in the incubation medium or the product ADP. Ethylenediaminetetraacetic acid, mercaptoethanol, and dithiothreitol are also ineffective in preventing loss of ATPase activity. Significantly, KPi at high concentration (greater than or equal to 200 mM) is effective in partially protecting F1 against inactivation. However, the most effective means of preventing Mg2+-induced inactivation of F1-ATPase activity is to rebind F1 to its F0 moiety in F1-depleted particles. When bound to F0, F1 is protected completely against divalent cation induced inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Immature megakaryocytes in the mouse: synergistic response to megakaryocyte potentiator, thrombopoietic stimulatory factor with interleukin 3

The in vitro biological activities of thrombopoietic stimulating factor, recombinant interleukin 3, and megakaryocyte potentiator from various sources were studied. Growth activities were assessed by the responsiveness of enriched populations of small, immature megakaryocytes to factor preparations by measuring increased numbers of acetylcholinesterase-positive cells and increased cell size as indices of megakaryocyte development. All factors stimulated optimum megakaryocyte growth at high concentrations. Immature megakaryocytes revealed the same responsiveness to titrated amounts of the various factors tested, with similar slopes to the dose-response curves. The activities of both thrombopoietic stimulating factor and megakaryocyte potentiator were additive when suboptimal doses were used. In contrast, low concentrations of recombinant interleukin 3 and thrombopoietic stimulating factor acted synergistically to stimulate an optimal response. The data indicate that at low and perhaps physiologically relevant concentrations, two classes of factors influence murine megakaryocyte development by different but related mechanisms.

Effects of auranofin and other antirheumatic drugs on human myelopoiesis in vitro

Leukopenia is one of the more serious side effects of auranofin (AF) therapy for rheumatoid arthritis. AF and its deacetylated form inhibited the development of macrophage and granulocytic colonies from progenitor cells in human bone marrow even at concentrations less than or equal to 10(-9)M. The disease suppressive activity of AF could result in part from the reduction of cell numbers in arthritic lesions and our findings provide a mechanism for this possibility. In contrast, other slow acting antirheumatic drugs, sulfasalazine, chloroquine and hydroxychloroquine, show partial inhibition of colony development but at concentrations of the order of 10(-5)M.

Ligand binding studies of the F1 moiety of rat liver ATP synthase: implications about the enzyme's structure and mechanism

F1-ATPase of rat liver was examined for its capacity to interact with both metal ions and nucleotides and for the effect of covalent ATPase inhibitors on these interactions. As isolated, rat liver F1 contains about 2 mol of Mg2+/mol of F1, 1 mol of which can be removed or exchanged. The remaining mole of Mg2+ per mole of F1 remains very tightly associated with F1 and is recovered in the alpha gamma fraction after cold denaturation. Rat liver F1 also contains as isolated a nearly equivalent amount of nucleotide (approximately 1.7 mol/mol of F1) which is readily removed by incubation at room temperature followed by column centrifugation. The "2 Mg2+ enzyme" binds almost 3 mol of 5'-adenylyl imidodiphosphate (AMP-PNP)/mol of F1 in the presence or absence of added divalent cation. When divalent cation is present as Co2+, an equivalent activator to Mg2+ in the ATPase reaction, 1 mol of F1 binds 3 mol of both AMP-PNP and Co2+. under these conditions, the very tight Mg2+ site remains loaded, the exchangeable Mg2+ site is replaced with AMP-PNPCo, and two additional AMP-PNPCo sites are filled. At this point, ADP can be loaded onto the enzyme as a fourth nucleotide at a site separate and distinct from the AMP-PNP sites. Significantly, rat liver F1 contains only a single readily detectable ADP binding site in the presence or absence of divalent cation.(ABSTRACT TRUNCATED AT 250 WORDS)

Haemopoietic growth factors stimulating murine megakaryocytopoiesis: interleukin-3 is immunologically distinct from megakaryocyte-potentiator

The biological and immunological properties of stimulators of in vitro murine megakaryocytopoiesis were studied using a heterologous anti-interleukin 3 (IL-3) serum. All megakaryocyte colony development was inhibited with the antiserum using three sources of IL-3, including WEHI-3 cell conditioned medium (WEHI-3CM), pokeweed mitogen-spleen conditioned medium (PWM-SCM) and recombinant IL-3. The data indicate that IL-3 is an absolute requirement for murine megakaryocyte colony development in this system. By comparison the antiserum abolished all myeloid colony growth stimulated by WEHI-3CM, but not PWM-SCM. The in vitro development of single megakaryocytes stimulated by a second putative growth factor, megakaryocyte-potentiator, was not inhibited by the antibody. The antiserum precipitated a 26 kd molecular weight protein from a radioiodinated sample of IL-3. No crossreactivity by the antiserum with other colony-stimulating factors (CSF) including CSF-1 and granulocyte-macrophage CSF was observed. The data indicates that IL-3 and megakaryocyte-potentiator are immunologically unrelated and provides further support that the two factors are separate molecules.

Pel, the protein that permits lambda DNA penetration of Escherichia coli, is encoded by a gene in ptsM and is required for mannose utilization by the phosphotransferase system

Mannose uptake and phosphorylation in Escherichia coli is catalyzed by the phosphoenolpyruvate:glycose phosphotransferase system (PTS). The mannose-specific complex of the PTS, designated IIMan, comprises lipid and two membrane proteins, II-AMan and II-BMan. The proteins are encoded by ptsM, located at approximately equal to 40 minutes on the E. coli chromosome. A different genetic marker, pel, maps with ptsM, and is required for lambda DNA penetration of the cytoplasmic membrane. Earlier studies suggested that both pel function and II-BMan are encoded by the same gene, while a different gene (also in ptsM) encodes II-AMan. In the present studies, a ptsM clone, pCS13, was isolated from an E. coli HindIII gene bank in pBR322 and restored both mannose termentation and pel+ function to ptsM mutants defective in II-BMan. Subclones of pCS13 show that two distinct genes, manY and manZ, encode the pel+ function and the II-BMan protein, respectively; each gene may have its own promoter; whereas the protein encoded by manY (Pel) alone seems sufficient for lambda sensitivity, all three gene products are required for mannose fermentation, transport of the mannose analogue 2-deoxyglucose, and phosphorylation of the latter by cytoplasmic membranes. Thus, Pel is required for function of the IIMan complex. The efficiency of the complex may depend on the ratio of Pel to IIMan.

An in situ immunoperoxidase staining procedure for human cell colonies grown in semi-solid agar culture

An adaptation of the immunoperoxidase staining procedure is described which enables the detection of antigens expressed by human hemopoietic cells grown in semi-solid agar culture. Positive staining was achieved using several different monoclonal antibodies recognizing an array of cell surface antigens on developing myeloid cells.

The pattern of HLA-DR and HLA-DQ antigen expression on clonable subpopulations of human myeloid progenitor cells

Three subpopulations of human myeloid progenitor cells (CFU-GM) can be distinguished by differences in their kinetics of development; the liquid phase pre-CFU-GM, the day 14 CFU-GM, and the day 7 CFU-GM. The relative cell membrane densities of the HLA-DR and HLA-DQ antigens expressed by the three subpopulations was investigated by comparing the amount of antibody required to deplete bone marrow cell preparations of each cell type. Three separate approaches were used--complement (C') cytotoxicity, antiglobulin/C'-cytotoxicity and immune rosette depletion. Similar results were obtained for all three procedures, although the latter two gave a tenfold greater sensitivity over the standard C'-cytotoxicity method. At saturating anti-HLA-DR antibody concentrations, 85% to 95% of cells within the three myeloid subpopulations were found to express HLA-DR antigens. However, the relative amount of HLA-DR expressed by these subpopulations increased from the pre-CFU-GM to the day 7 CFU-GM. The expression of HLA-DQ antigens was considerably lower and could only be detected by using the more sensitive procedures. Only 50% of day 7 and 14 CFU-GM progenitor cells expressed detectable HLA-DQ antigens, whereas a greater proportion (80%) of the pre-CFU-GM were HLA-DQ positive. The pattern of HLA-DQ expression on these clonable precursors was quite distinct and opposite to the cell membrane density of the HLA-DR antigens. Because these three progenitor cell populations are thought to be linked in differentiation sequence, these results provide indirect support for the hypothesis that HLA class II antigens are implicated in regulatory mechanisms during normal myeloid cell differentiation.

Biochemical characterization of an in-vitro murine megakaryocyte growth activity: megakaryocyte potentiator

The biochemical properties of an in-vitro megakaryocyte growth factor called megakaryocyte potentiator (Mk-POT) were investigated. P388D1 cell conditioned medium (P388D1 CM), was used as the source of Mk-POT. The potentiator activity had an apparent mol. wt of 21 kilodaltons (kd) by gel filtration and was eluted from DEAE-Sepharose pH 8.0 with 0.15 M NaCl. Chromatofocusing revealed three active species with apparent pIs of 4.0, 5.5 and above 6.0. Most Mk-POT activity does not bind to Concanavalin A-Sepharose. Mk-POT activity is sensitive to reduction by dithiothreitol and temperatures above 90 degrees C. Treatment with trypsin, alpha-chymotrypsin and pronase also reduced the Mk-POT activity, but it was not destroyed by RNase A or neuraminidase. It is precipitated in ammonium sulphate solutions of between 60 to 70% saturation, and by 80% ethanol. The Mk-POT activity is stable in solutions of pH 5.0-9.0. The data presented here suggest that megakaryocyte potentiator is either heterogeneous in its properties or more than one molecular species may express the in-vitro Mk-POT activity found in P388D1 CM.

Treatment of chronic knee effusions with 90yttrium-correlation of in vitro radiation and chemical effects with clinical results at three and six months

Twenty seven knees, mainly of rheumatoid patients, received intra-articular 90Y for chronic effusions; 24% were effusion-free at 6 months. In vitro chemical, radiation (32P-induced), and combined effects of cold (non-radioactive) yttrium and 32P on synovial fluid mononuclear cells, failed to show any significant correlation with subjective and/or objective clinical effects at 3 or 6 months. If 90Y exerts its therapeutic effect via these cells, it probably does so other than by a direct effect on mononuclear cell viability.

In vitro inhibition of myelopoiesis by gold salts and D-penicillamine

Leukopenia is one of the more serious side effects of gold and D-penicillamine therapy. We report that gold salts (gold thiomalate, gold chloride and gold thioglucose) and D-penicillamine suppressed the in vitro development of colonies of myeloid cells (macrophage, granulocyte and megakaryocyte) from progenitor cells in murine bone marrow; these drugs were also effective in inhibiting the development of macrophage and granulocytic colonies in human bone marrow. The drugs generally required concentrations of 10(-5) M in the murine system, whereas they were active at 10(-7)-10(-8) for the human progenitor cells. The disease suppressive activity of gold salts and D-penicillamine could result in part from the reduction of cell numbers in arthritic lesions; our findings would provide a mechanism for this possibility.

Dose rates from patients having nuclear medicine investigations

Dose rates have been measured at 0.1 m, 0.5 m and 1.0 m from patients in a Nuclear Medicine Department. Data are presented for a variety of Nuclear Medicine procedures using doses of radiopharmaceuticals within the recommendations of the administration of Radioactive Substances Advisory Committee (ARSAC). The corresponding figures when the patient left the department, and the time average dose rate over the next 8 h were calculated. At 1.0 m the dose rates do not exceed 7.5 microSv h-1, and at 0.5 m the time average dose rate does not exceed 60 microSv h-1. Assuming that the nurse is as close to the patient as 0.1 m for 20 min in a working day, the accumulated dose over a working day would not exceed 60 microSv.

Murine megakaryocyte colony stimulating factor: its relationship to interleukin 3

A protocol for the partial purification of murine megakaryocyte colony stimulating factor from WEHI-3 cell conditioned medium is described. The procedure involving separation by anion exchange chromatography and molecular sieving on Sephadex G100, gave a 260-fold purification over starting material, as determined by in-vitro megakaryocyte colony formation. Fifty percent of maximum colony numbers were obtained at a dose of 1 microgram protein/ml. Electrophoretic analysis of the partially purified preparation followed by silver nitrate staining revealed four major protein bands with apparent molecular weights of 67 Kd, 43 Kd, 38 Kd and 28 Kd. All megakaryocyte colony stimulating activity and interleukin 3 activity was found in the 22-25 Kd fraction from a preparative SDS-polyacrylamide gel using non-reducing conditions, a molecular weight range that coincided with the 28-Kd molecule obtained when reducing conditions were employed.