Progressive multifocal leukoencephalopathy post ibrutinib therapy in relapsed chronic lymphocytic leukaemia

Progressive multifocal leukoencephalopathy (PML) is a generally fatal infection of the cerebrum by the JC virus. It occurs in a range of primary and secondary immunosuppressed states and has become more common with AIDS and increasing the use of immunosuppressive therapies. Recently, Ibrutinib, a Bruton's Tyrosine Kinase Inhibitor (BTKi), has also been associated with PML. Here, we describe the case of a 77-year-old man treated for relapsed Chronic Lymphocytic Leukemia (CLL) with Ibrutinib, who eventually developed a fatal cerebellar granule cell variant of PML confirmed on autopsy. The case adds to the growing body of literature finding such an association with BTKis and highlights the importance of clinical vigilance in patients receiving such therapy.

Beyond cones: an improved model of whisker bending based on measured mechanics and tapering

The sense of touch is represented by neural activity patterns evoked by mechanosensory input forces. The rodent whisker system is exceptional for studying the neurophysiology of touch in part because these forces can be precisely computed from video of whisker deformation. We evaluate the accuracy of a standard model of whisker bending, which assumes quasi-static dynamics and a linearly tapered conical profile, using controlled whisker deflections. We find significant discrepancies between model and experiment: real whiskers bend more than predicted upon contact at locations in the middle of the whisker and less at distal locations. Thus whiskers behave as if their stiffness near the base and near the tip is larger than expected for a homogeneous cone. We assess whether contact direction, friction, inhomogeneous elasticity, whisker orientation, or nonconical shape could explain these deviations. We show that a thin-middle taper of mouse whisker shape accounts for the majority of this behavior. This taper is conserved across rows and columns of the whisker array. The taper has a large effect on the touch-evoked forces and the ease with which whiskers slip past objects, which are key drivers of neural activity in tactile object localization and identification. This holds for orientations with intrinsic whisker curvature pointed toward, away from, or down from objects, validating two-dimensional models of simple whisker-object interactions. The precision of computational models relating sensory input forces to neural activity patterns can be quantitatively enhanced by taking thin-middle taper into account with a simple corrective function that we provide.

Irinophore C, a novel nanoformulation of irinotecan, alters tumor vascular function and enhances the distribution of 5-fluorouracil and doxorubicin

PURPOSE

To examine the antitumor effects of Irinophore C, a nanopharmaceutical formulation of irinotecan, on the tissue morphology and function of tumor vasculature in HT-29 human colorectal tumors.

EXPERIMENTAL DESIGN

Fluorescence microscopy was used to map and quantify changes in tissue density, tumor vasculature, hypoxia, and the distribution of Hoechst 33342, a perfusion marker, and the anticancer drug, doxorubicin. Noninvasive magnetic resonance imaging was used to quantify Ktrans, the volume transfer constant of a solute between the blood vessels and extracellular tissue compartment of the tumor, as a measure of vascular function. Following treatment with Irinophore C, 19F magnetic resonance spectroscopy was used to monitor the delivery of 5-fluorouracil (5-FU) to the tumor tissue, whereas scintigraphy was used to quantify the presence of bound [14C]5-FU.

RESULTS

Irinophore C decreased cell density (P = 8.42 x 10(-5)), the overall number of endothelial cells in the entire section (P = 0.014), tumor hypoxia (P = 5.32 x 10(-9)), and K(trans) (P = 0.050). However, treatment increased the ratio of endothelial cells to cell density (P = 0.00024) and the accumulation of Hoechst 33342 (P = 0.022), doxorubicin (P = 0.243 x 10(-5)), and 5-FU (P = 0.0002) in the tumor. Vascular endothelial growth factor and interleukin-8, two proangiogenic factors, were down-regulated, whereas the antiangiogenic factor TIMP-1 was up-regulated in Irinophore C-treated tumors.

CONCLUSIONS

Irinophore C treatment improves the vascular function of the tumor, thereby reducing tumor hypoxia and increasing the delivery and accumulation of a second drug. Reducing hypoxia would enhance radiotherapy, whereas improving delivery of a second drug to the tumor should result in higher cell kill.

Modulation of cancer cell survival pathways using multivalent liposomal therapeutic antibody constructs

Various methods have been explored to enhance antibody-based cancer therapy. The use of multivalent antibodies or fragments against tumor antigens has generated a great deal of interest, as various cellular signals, including induction of apoptosis, inhibition of cell growth/survival, or internalization of the surface molecules, can be triggered or enhanced on extensive cross-linking of the target/antibody complex by the multivalent form of the antibody. The goal of the studies reported here was to develop multivalent antibody constructs via grafting of antibody molecules onto liposome membranes to enhance antibody activity. Using trastuzumab and rituximab as examples, up to a 25-fold increase in the antibody potency in cell viability assay was observed when the antibodies were presented in the multivalent liposome formulation. Key cell survival signaling molecules, such as phosphorylated Akt and phosphorylated p65 nuclear factor-kappaB, were down-regulated on treatment with multivalent liposomal trastuzumab and liposomal rituximab, respectively. Potent in vivo antitumor activity was shown for liposomal trastuzumab. The data presented here showed the potential of liposome technology to enhance the therapeutic effect of antibodies via a mechanism that modulates cell survival through clustering of the target/antibody complex.

Non-invasive evaluation of tumour hypoxia in the Shionogi tumour model for prostate cancer with 18F-EF5 and positron emission tomography

OBJECTIVE

To evaluate hypoxia non-invasively in androgen-dependent (AD), regressing (6-days after castration, RG) and androgen-independent (AI) Shionogi tumours, using the radiolabelled tracer for hypoxia, 18F-EF5, and positron emission tomography (PET).

MATERIALS AND METHODS

Groups of mice bearing AD, RG and AI Shionogi tumours were co-injected with 18F-EF5 and unlabelled EF5. The mice were imaged non-invasively with PET to examine the accumulation of 18F-EF5 in hypoxic regions of the tumour. The tumours were subsequently placed in a gamma-counter, or disaggregated for flow cytometry, to determine the levels of 18F-EF5 and the percentage of hypoxic cells present in the tumour, respectively.

RESULTS

The mean (sd) levels of hypoxia in AD Shionogi tumours decreased significantly 6 days after androgen ablation as measured by flow cytometry, from 17.1 (4.77) to 1.74 (0.46)% (P=0.003). There were no significant differences in the levels of 18F-EF5 in the tissue between AD and RG tumours using region-of-interest analysis of PET images or gamma-counting, although the differences were significant when measured by flow cytometry. However, mean (sd) levels of hypoxia in AI Shionogi tumours were significantly higher than in AD tumours regardless of the analysis method; PET, 10.5 (4.93)x10(-5)) Bq/cm2 (P=0.017), flow cytometry, 42.98 (3.35)% (P<0.001), well count, 6.81 (1.17)x10(4) and 13.1 (1.99)x10(4) cpm/g, for AD and AI tumours, respectively (P<0.001).

CONCLUSIONS

Differences in hypoxia between AD and AI, but not RG, Shionogi tumours can be detected non-invasively with 18F-EF5 and PET. As prostate tumours are hypoxic and the oxygen levels can change with androgen ablation, noninvasive imaging of hypoxia with PET and 18F-EF5 might ultimately have a prognostic and/or diagnostic role in the clinical management of the disease.

Genome-wide Expression Analyses of Campylobacter jejuni NCTC11168 Reveals Coordinate Regulation of Motility and Virulence by flhA

We examined two variants of the genome-sequenced strain, Campylobacter jejuni NCTC11168, which show marked differences in their virulence properties including colonization of poultry, invasion of Caco-2 cells, and motility. Transcript profiles obtained from whole genome DNA microarrays and proteome analyses demonstrated that these differences are reflected in late flagellar structural components and in virulence factors including those involved in flagellar glycosylation and cytolethal distending toxin production. We identified putative sigma(28) and sigma(54) promoters for many of the affected genes and found that greater differences in expression were observed for sigma(28)-controlled genes. Inactivation of the gene encoding sigma(28), fliA, resulted in an unexpected increase in transcripts with sigma(54) promoters, as well as decreased transcription of sigma(28)-regulated genes. This was unlike the transcription profile observed for the attenuated C. jejuni variant, suggesting that the reduced virulence of this organism was not entirely due to impaired function of sigma(28). However, inactivation of flhA, an important component of the flagellar export apparatus, resulted in expression patterns similar to that of the attenuated variant. These findings indicate that the flagellar regulatory system plays an important role in campylobacter pathogenesis and that flhA is a key element involved in the coordinate regulation of late flagellar genes and of virulence factors in C. jejuni.

Hospitalized congestive heart failure patients with preserved versus abnormal left ventricular systolic function: clinical characteristics and drug therapy

PURPOSE

To compare clinical characteristics of and pharmacologic therapy for hospitalized patients with congestive heart failure (CHF) and left ventricular systolic dysfunction or normal left ventricular systolic function.

PATIENTS AND METHODS

Medical records were reviewed for all patients discharged with a principal diagnosis of CHF from a university hospital and a community hospital between September 1, 1991 and August 31, 1992. Pertinent medical history items and prescribed drug therapies at discharge were recorded for each patient's first calendar year admission. Patients were categorized as having either normal left ventricular systolic function or systolic dysfunction based on the results of echocardiography and radionuclide angiography or contrast ventriculogram.

RESULTS

Of 298 patients with CHF, 92 (31%) had normal left ventricular systolic function. Patients with normal systolic function were older, were more often women, were less likely to have a history of coronary artery disease, and were more likely to have a history of hypothyroidism than patients with systolic dysfunction. However, the prevalence of clinical characteristics overlapped considerably between the two groups. Among patients with systolic dysfunction, 79% were discharged on a therapeutic regimen of digoxin, 65% on an angiotensin-converting enzyme inhibitor, and 26% on either a beta-blocker or a calcium channel blocker. Among patients with normal systolic function, 50% were discharged on a regimen of a beta-blocker or a calcium channel blocker and 38% were discharged on digoxin. Twenty-six percent of patients with normal systolic function and without a history of atrial fibrillation were discharged on a digoxin regimen.

CONCLUSION

Hospitalized CHF patients with normal left ventricular systolic function and those with diminished left ventricular systolic function share many clinical features. Since recommended drug therapy and prognosis differ, our data underscore the importance of diagnostic testing to assess left ventricular systolic function. Drug therapy for CHF patients provides a major challenge for quality-of-care improvement.

Identification of intraocular lens-adsorbed proteins in mammalian in vitro and in vivo systems

OBJECTIVE

Mammalian in vitro and in vivo systems were used to study the protein-adsorbing potential of intraocular lenses (IOLs).

METHODS

Intraocular lenses composed of polymethyl methacrylate optics with polypropylene haptics were incubated in rabbit plasma for 3 hours (in vitro grouping) or implanted in rabbit eyes for 48 hours (in vivo grouping). Lens-adsorbed proteins from both experimental groupings were eluted with sodium dodecyl sulfate and identified by Western Blot analyses.

RESULTS

The adsorbed protein layer was composed of at least six different proteins: albumin, complement C3 fragments, IgG, fibrinogen/fibrin (as a fibrin clot in vivo), fibronectin, and transferrin. Of the identified components, albumin, IgG, fibronectin, and fibrinogen were the predominant protein species on the in vitro IOLs, while fibronectin and fibrin were on the in vivo IOLs.

CONCLUSIONS

The composition of the protein layer has the potential to alter the biological property of IOLs.

Nicardipine in heart failure: distinguishing its acute beneficial from its chronic effects

Concern over negative inotropic effects has limited the use of calcium blockers in patients with congestive heart failure. Nicardipine, a second generation dihydropyridine calcium channel blocker, has demonstrated positive hemodynamic effects in short-term therapy in patients with congestive heart failure. Prolonged use of calcium channel blockers remains contraindicated in patients with congestive heart failure due to the potential for activation of the renin-angiotensin system. However, acute intravenous nicardipine administration has important clinical applications (as in the management of surgical hypertension or hypertensive emergencies). Nicardipine may be safely used for these indications even in the presence of congestive heart failure.

Dipeptide inhibitors of ubiquitin-mediated protein turnover prevent growth factor-induced neurite outgrowth in rat pheochromocytoma PC12 cells

Dipeptide inhibitors of the ubiquitin-dependent proteolysis pathway governed by N-terminal recognition (N-end rule) in reticulocyte lysates significantly suppress NGF- and bFGF-induced neurite outgrowth in rat pheochromocytoma PC12 cells, but do not cause retraction of already formed neurites. Peptides which do not inhibit proteolysis are also without effect on PC12 cell differentiation. Suppression of neurite outgrowth is readily reversible upon removal of the inhibitors. These data demonstrate a requirement for specific protein turnover in the process of neuron-like differentiation in PC12 cells and provide the first demonstration of a physiological role for the N-end rule.

Anomeric specificity of glucose effect on cAMP, fructose 1,6-bisphosphatase, and trehalase in yeast

The addition of beta-D-glucose (final concentration, 50 mM) to a cell suspension of Saccharomyces cerevisiae in stationary phase caused a rapid 4-fold increase in the concentration of cAMP, while a 2-fold increase of cAMP was observed by the addition of alpha-D-glucose. beta -D-Glucose was also more effective than alpha-D-glucose in the inactivation of fructose 1,6-bisphosphatase and the activation of trehalase. These results, taken together with the previous report that alpha-D-glucose is transported more rapidly than beta-D-glucose in Saccharomyces cerevisiae, do not support the view currently proposed by some investigators that cotransport of D-glucose with protons causes the depolarization of the cell membrane, resulting in the activation of adenylate cyclase. The present data, however, provides supporting evidence for the view that cAMP-dependent protein kinase is implicated in the inactivation of fructose 1,6-bisphosphatase and the activation of trehalase.

An altered adenylate cyclase in cdc35-1 cell division cycle mutant of yeast

Adenylate cyclase activity was studied in Saccharomyces cerevisiae's cell division cycle (cdc) mutant 35-1. The temperature sensitive mutant cdc35-1 was previously mapped as an allele of cyr, the adenylate cyclase gene. However, the adenylate cyclase activities of membranes prepared from cdc35-1 were not thermosensitive. The adenylate cyclase activity of cdc35-1 was found to have an altered Mn2+ dependency and did not respond to Gpp(NH)p stimulation. These results suggest that cdc35-1 mutation may not be at the catalytic site but at a site where adenylate cyclase interacts with regulatory proteins.

Catabolite inactivation of fructose 1,6-bisphosphatase and cytoplasmic malate dehydrogenase in yeast

Catabolite inactivation of fructose 1,6-bisphosphatase and cytoplasmic malate dehydrogenase was studied using the protease-deficient and vacuole-defective yeast strain pep4-3. The catabolite inactivation of fructose 1,6-bisphosphatase in pep4-3 was found to have a normal first inactivation step but with a defective second proteolytic step. In contrast, catabolite inactivation of cytoplasmic malate dehydrogenase was normal in pep4-3. These results suggest that the proteolytic pathways utilized in the hydrolysis of the two enzymes may be different and that proteolysis of fructose 1,6-bisphosphatase may require functional vacuoles while proteolysis of cytoplasmic malate dehydrogenase may not.

Purification and phosphorylation of fructose-1,6-bisphosphatase from Kluyveromyces fragilis

Fructose-1,6-bisphosphatase from the yeast Kluyveromyces fragilis was found to have an apparent Mr = 155,000 and to be composed of four Mr = 35,000 subunits. The extent and rate of phosphorylation of fructose-1,6-bisphosphatase (Fru-1,6-P2) by yeast cAMP-dependent protein kinase were dependent on fructose-1,6-bisphosphatase inhibitors, 5'-AMP and fructose 2,6-bisphosphate (Fru-2,6-P2). In the absence of inhibitor, the enzyme was slowly phosphorylated with a maximum incorporation of 1 mol of phosphate/mol of enzyme. The presence of both inhibitors greatly increased the phosphorylation rate with a maximum incorporation of 2 mol of phosphate/mol of enzyme. The presence of only one inhibitor led to an intermediate rate of phosphorylation with 2 mol of phosphate incorporated/mol of enzyme. There was no significant change in enzymatic activity after phosphorylation. The estimated sedimentation coefficient of fructose-1,6-bisphosphatase was lowered by 5'-AMP from 8.2 to 5.7 while Fru-2,6-P2 increased the S value to 8.5. The presence of either Fru-1,6-P2 or Fru-2,6-P2 prevented the 5'-AMP lowering of S value. The susceptibility of enzyme to partial tryptic digestion was not changed by the presence of 5'-AMP. The presence of both Fru-2,6-P2 and 5'-AMP led to the protection of Mr = 35,000 subunit from tryptic digestion while Fru-2,6-P2 alone led to a protection of an Mr = 30,000 peptide fragment. This peptide fragment did not contain the phosphorylation sites. Our results suggest that the rapid regulation of fructose-1,6-bisphosphatase following glucose addition is controlled mainly by enzyme inhibitors.

Enzymic synthesis and cofactor activity of 3'-pyrophosphocoenzyme A

The 3'-pyrophosphate derivative of CoA was synthesized by using the excreted 5'-to-3' pyrophosphoryl-transferring enzyme from Streptomyces adephospholyticus and ATP as donor and dephospho-CoA as acceptor. Cofactor activity of this new coenzyme A derivative was tested with Clostridium kluyveri phosphotransacetylase and hog heart succinic thiokinase. With the phosphotransacetylase, 3'-pyrophospho-CoA was found to be twice as active as CoA whereas dephospho-CoA was inactive. However, succinic thiokinase utilized all three types of CoA equally well. Adenosine 5'-monophosphate 3'-pyrophosphate also was synthesized and used as an analog of adenosine 5'-monophosphate 3'-monophosphate in the dog liver's sulfotransferase-catalyzed sulfate transfer from p-nitrophenyl sulfate to phenol. In contrast to the pyrophospho derivative of coenzyme A, adenosine 5'-monophosphate 3'-pyrophosphate was inactive as a cofactor.

Guanosine 5'-triphosphate, 3'-diphosphate 5'-phosphohydrolase. Purification and substrate specificity

The regulatory nucleotide guanosine 5'-diphosphate, 3'-diphosphate (ppGpp) and its precursor guanosine 5'-triphosphate, 3'-diphosphate (pppGpp) are accumulated during stringent response in bacterial cells. The enzyme pppGpp-5'-phosphohydrolase, which catalyzes the conversion of pppGpp to ppGpp, was partially purified from Escherichia coli. It has Mr = 140,000 and an apparent Km of 0.11 mM for pppGpp. It requires Mg2+ and a monovalent cation. NH4+ is preferred over K+, while Na+ is inactive. The enzyme does not hydrolyze GTP, ATP, pppApp, or ppGpp. It is also not effectively inhibited by these nucleotides. pppGpp-5'-phosphohydrolase hydrolyzes the 3'-monophosphate analog pppGp equally well (apparent Km of 0.13 mM), yielding the recently identified MS III nucleotide (ppGp). pppGpp-5'-phosphohydrolase does not have RNA 5'-terminal gamma-phosphatase activity; however, 5'-terminal phosphates are released by pppGpp-5'-phosphohydrolase when the GTP-terminated RNA chains are first converted into oligonucleotides by RNase A treatment. pppGpp-5'-phosphohydrolase was found to actively hydrolyze the dinucleotide fragment pppGpNp but exhibited very low activity toward longer chain fragments. The 3'-unphosphorylated dinucleotide pppGpN was, however, not hydrolyzed. The ability of pppGpp-5'-phosphohydrolase to hydrolyze pppGpp, pppGp, and pppGpNp, but not pppG and pppGpN, indicates that pppGpp-5'-phosphohydrolase is rather nonspecific toward the 3'-OH substitutions of the substrates although a free, unsubstituted phosphate group at the 3'-OH position is essential.

Phosphorylation of the regulatory subunit of yeast cAMP-dependent protein kinase

In vitro phosphorylation of the regulatory subunit of yeast cAMP-dependent protein kinase was studied. The cAMP-binding regulatory subunit (R subunit) can be multiply phosphorylated. Three distinct phosphorylation sites were inferred from the different ATP concentrations required for phosphorylation and from the presence of two discrete mobility shifts in NaDodSO4/polyacrylamide gel electrophoresis of the R subunit on phosphorylation. Limited tryptic digestion of the phosphorylated R subunit showed that a Mr 37,000 cAMP-binding peptide contained one of the phosphorylation sites and that a separate Mr 12,000 peptide contained another phosphorylation site. The yeast R subunit is therefore similar to the type II R subunit of mammalian origin, although it has a larger Mr (64,000 vs. 58,000) and is multiply phosphorylated. In vivo, both phosphorylated and unphosphorylated forms of the R subunit were found in cells grown in lactate or to stationary phase in 1.5% glucose, while cells grown in 5% glucose contained the unphosphorylated form.

Activation of ppGpp-3'-pyrophosphohydrolase by a supernatant factor and ATP

The breakdown of guanosine 5'-diphosphate, 3'-diphosphate (ppGpp) into GDP and PPi is catalyzed by a Mn2+-dependent 3'-pyrophosphohydrolase, the translation product of the spoT gene. The escherichia coli enzyme is normally found to be associated with the "crude" ribosome fraction. It is reported here that the guanosine 5'-diphosphate, 3'-diphosphate 3'-pyrophosphohydrolase activity in this fraction is activated by ATP in the presence of a relatively heat-stable, low molecular weight, supernatant factor (BS100). This stimulation is not due to a removal of reaction products such as by the phosphorylation of GDP to GTP or by the hydrolysis of PPi. Hydrolysis of ATP is probably required because neither adenosine 5'-(3-thio)triphosphate nor adenosine 5'-(beta, gamma-imido)triphosphate can substitute for ATP. Levallorphan, a morphine analog, which had been shown to inhibit in vivo ppGpp degradation, inhibits specifically the stimulation of ppGpp hydrolysis by ATP and the supernatant factor. The possible relationship of this system and the in vivo energy-dependent control of ppGpp degradation is discussed.

In vitro degradation of guanosine 5'-diphosphate, 3'-diphosphate

The degradation of guanosine 5'-diphosphate,3'-diphosphate (ppGpp) by the "crude" ribosomal fraction of Escherichia coli CP78 (rel+, spoT+) was demonstrated and characterized. When the 3'-pyrophosphoryl group of ppGpp was hydrolyzed, the primary degradation product was 5'-GDP. Phosphorylation of ppGpp to guanosine 5'-triphosphate,3'-diphosphate (pppGpp) prior to degradation was not necessary. The degradation process required Mn2+ and was inhibited by EDTA. Levallorphan, an inhibitor of in vivo ppGpp degradation, also inhibited ppGpp degradation by the crude ribosome. Thiostrepton and tetracycline did not have any inhibitory effect, indicating that the reaction is not a reversal of pyrophosphorylation catalyzed by the stringent factor/ribosome complex. Crude ribosome fractions from E. coli NF161 and NF162, both spoT-, contained little degrading activity, but similar fractions of E. coli CP79, a relA- and spoT+ strain, contained ppGpp degrading activity.

Purification and properties of guanosine 5', 3'-polyphosphate synthetase from Bacillus brevis

A ribosome-independent guanosine 5',3'-polyphosphate synthetase has been highly purified from Bacillus brevis (ATCC 8185). The enzyme has a molecular weight of 55,000, as measured by sucrose density gradient centrifugation. Like the ribosome-connected stringent factor of Escherichia coli, it catalyzes the synthesis of the guanosine 5', 3'-polyphosphates by a pyrophosphoryl transfer mechanism from adenosine triphosphate (ATP) to guanosine di- or triphosphates (GDP, GTP). It has an apparent Km of 0.14 mM for GDP and 0.77 mM for GTP, and is specific for the guanosine ribonucleotides as pyrophosphoryl acceptors. Several ATP analogues were tested for their ability to donate the pyrophosphoryl group. Mg2+ was required as a counter ion for the nucleotide substrate; however, an excess of Mg2+ was inhibitory. The property of the B. brevis enzyme is compared with the ribosome-linked enzyme of E. coli and an extracellular enzyme excreted by several types of Streptomyces reported upon recently.

A ribosome-independent, soluble stringent factor-like enzyme isolated from a Bacillus brevis

A ribosome-independent synthesis of guanosine 5',3'-polyphosphates has been found in the soluble fraction of Bacillus brevis (ATCC 8185) extracts. The partially purified enzyme catalyzes the formation of both guanosine 5'-diphosphate 3'-diphosphate and guanosine 5'-triphosphate 3'-diphosphate, does not require 20% methanol to stimulate the rate of reaction, and is not stimulated by complexing with ribosomes of either Escherichia coli or B. brevis. The B. brevis enzyme system is not inhibited by RNase A or thiostrepton, and is only slightly inhibited by tetracycline. The pyrophosphoryl donor specificity of the B. brevis enzyme is similar to that of the E. coli ribosome-stringent factor system.

Nucleotide specificity of stringent factor and the synthesis of analogs of guanosine 5'-diphosphate 3'-diphosphate and guanosine 5'-triphosphate 3'-diphosphate

The ribosome-dependent stringent factor reaction was found to be nonspecific with regard to the number of phosphate groups linked to the 5' position of guanosine nucleotides. Both GMP and guanosine 5'-tetraphosphate could accept a pyrophosphoryl group from ATP although at a much lower rate than GDP or GTP. Guanosine 5'-monophosphate 3'-diphosphate and guanosine 5'-tetraphosphate 3'-diphosphate were the products of these reactions. Furthermore, 3'-linked analogs of guanosine 5'-diphosphate 3'-diphosphate and guanosine 5'-triphosphate 3'-diphosphate were synthesized from the corresponding ATP analog, adenosine 5'-O-(3-thiotriphosphate). The stringent factor catalyzed reverse reaction was found to be specific for guanosine 5'-diphosphate 3'-diphosphate, and was essentially inactive to the isomeric form, guanosine 5'-diphosphate 2'-diphosphate.

Reversibility of the pyrophosphoryl transfer from ATP to GTP by Escherichia coli stringent factor

The stringent factor-catalyzed, ribosome-dependent synthesis of guanosine polyphosphates is found to be reversible. The reverse reaction specifically requires 5'-AMP as the pyrophosphoryl acceptor, and guanosine 5'-triphosphate-3'-diphosphate is preferentially utilized as the pyrophosphoryl donor. The primary products of the reaction are GTP and ATP. The reverse reaction is strongly inhibited by the antibiotics thiostrepton and tetracycline, and by ATP and beta-gamma-methylene-adenosine-triphosphate, but not by ADP, GTP, and GDP. The reverse reaction occurs under conditions for nonribosomal synthesis. The overall reaction for stringent factor-catalyzed guanosine polyphosphate formation may thus be formulated: (p)pp5'G + ppp5'A right harpoon over left harpoon (p)pp5'G3'pp + p5'A.

Nonribosomal synthesis of guanosine 5',3'-polyphosphates by the ribosomal wash of stringent Escherichia coli

A factor in the ribosomal wash of stringent strains of E. coli was identified by Haseltine et al. as a complement to the ribosomal system for the synthesis of the magic spot compounds of Cashel and Gallant. This factor has been found, in the absence of ribosomes, to catalyze the enzymatic pyrophosphoryl transfer from ATP to GTP or GTP in the formation of magic spot I and magic spot II, the guanosine tetra- and pentaphosphates (ppGpp and pppGpp), respectively. The enzyme, which normally requires the presence of the ribosome-tRNA-mRNA complex for activity, catalyzes a very slow synthesis that is stimulated tenfold by 20% methanol. The temperature optimum of the methanol-stimulated system is 25-30 degrees and activity is drastically depressed at 37 degrees , presumably by inactivation. Catalysis is linear with enzyme concentration and with time for the first 3 hr; during this period 25% of the added GTP is converted. The nonribosomal system is distinguished from the ribosomal system by having a lower Mg(++) and a higher NH(4) (+) optimum. The two systems differ in their response to antibiotics: thiostrepton strongly inhibits the ribosomal system but has no effect on the nonribosomal system.

Identification of the synthesis of guanosine tetraphosphate (MS I) as insertion of a pyrophosphoryl group into the 3'-position in guanosine 5'-diphosphate

The phosphate transfer system of Haseltine et al., consisting of a ribosomal wash obtained from a stringent strain of Escherichia coli, washed ribosomes, GTP, and ATP, was used to prepare large quantities of guanosine tetra- and pentaphosphates, the magic spot compounds MS I and MS II of Cashel and Gallant. In our hands, the Haseltine et al. system yielded predominantly guanosine tetraphosphate, ppGpp. This system was used exclusively in the described experiments, with ATP labeled with (32)P in the beta- and gamma-positions as donor. The beta-label was found to produce a ppG[unk]p and the gamma-label a ppGp 0001000 1101011 0011100 0011100 1101011 0001000 0000000 0101100 1110010 0100001 0100001 0100001 0110010 0101100 0100000 0100000 1110000 . Furthermore, [(3)H]GDP + [gamma-(32)P]ATP yielded ppGpp in a (3)H:(32)P ratio of 1:1. The results indicate a transfer of the terminal pyrophosphoryl group of ATP as a unit. The position of the transferred pyrophosphoryl was assayed for by preparation of pG from ppGp with Zn(++)-activated inorganic pyrophosphatase from yeast. The pG was then assayed with 3'-nucleotidase, which liberated practically all the labeled phosphate. This result indicate that the phosphate transfer from ATP to GDP yields guanosine 5'-diphosphate-3'-diphosphate.