Design and kinetic characterization of multisubstrate inhibitors of dopamine beta-hydroxylase

The synthesis and kinetics characterization of a new class of dopamine beta-hydroxylase (DBH; EC 1.14.17.1) inhibitor, 1-(4-hydroxybenzyl)imidazole-2-thiol, is reported. These inhibitors, which incorporate a phenethylamine substrate mimic and an oxygen mimic into a single molecule, exhibit both the kinetic properties and the potency (Kis approximately 10(-9) M) expected for a multisubstrate inhibitor and are therefore classified as such. Steady-state kinetic experiments with these multisubstrate inhibitors and their substructural analogues support the recently proposed pH-dependent changes in substrate binding order [Ahn, N., & Klinman, J. P. (1983) Biochemistry 22, 3106] and a mechanism whereby the inhibitor binds specifically to the reduced Cu+ form of enzyme at both the phenethylamine substrate site and the active-site copper atom(s). A Yonetani-Theorell double-inhibition experiments indicates mutually exclusive binding of the inhibitor substructures p-cresol and 1-methylimidazole-2-thiol to suggest an extremely short intersite distance between the phenethylamine binding site and the active-site copper atom(s).     

Characterization of Rous sarcoma virus-related sequences in the Japanese quail.

We detected sequences related to the avian retrovirus Rous sarcoma virus within the genome of the Japanese quail, a species previously considered to be free of endogenous avian leukosis virus elements. Using low-stringency conditions of hybridization, we screened a quail genomic library for clones containing retrovirus-related information. Of five clones so selected, one, lambda Q48, contained sequence information related to the gag, pol, and env genes of Rous sarcoma virus arranged in a contiguous fashion and spanning a distance of approximately 5.8 kilobases. This organization is consistent with the presence of an endogenous retroviral element within the Japanese quail genome. Use of this element as a high-stringency probe on Southern blots of genomic digests of several quail DNA demonstrated hybridization to a series of high-molecular-weight bands. By slot hybridization to quail DNA with a cloned probe, it was deduced that there were approximately 300 copies per diploid cell. In addition, the quail element also hybridized at low stringency to the DNA of the White Leghorn chicken and at high stringency to the DNAs of several species of jungle fowl and both true and ruffed pheasants. Limited nucleotide sequencing analysis of lambda Q48 revealed homologies of 65, 52, and 46% compared with the sequence of Rous sarcoma virus strain Prague C for the endonuclease domain of pol, the pol-env junction, and the 3'-terminal region of env, respectively. Comparisons at the amino acid level were also significant, thus confirming the retrovirus relatedness of the cloned quail element.     

Psychological problems associated with diagnosis and treatment of lymphomas. I: Retrospective study.

Patients treated for Hodgkin''s disease and non-Hodgkin''s lymphoma have a better prognosis than other patients with cancer so may have a lower prevalence of psychological and social morbidity. Trained interviewers used standardised methods to assess 90 patients at a mean of 32 months after the diagnosis of Hodgkin''s disease or non-Hodgkin''s lymphoma. Chemotherapy and radiotherapy had commonly caused adverse effects including hair loss, vomiting, nausea, and loss of appetite. Although most patients were free of disease and not receiving treatment at follow up, some still suffered from a lack of energy (31 patients), loss of libido (19), irritability (22), and tiredness (19); 30 patients complained of continued impairment of thinking or disturbance of short term memory. After diagnosis 21 patients had suffered from an anxiety state or depressive illness, or both, while 27 had experienced borderline anxiety or depression, or both. Mood disturbance was positively correlated with adverse effects of treatment, particularly those affecting the gastrointestinal tract. Social adjustment was less affected, but failure to return to work, or a long delay in returning to work, and a persistent lack of interest in leisure activities gave cause for concern. These findings of substantial psychiatric and social morbidity in patients with Hodgkin''s disease and non-Hodgkin''s lymphoma prompted a prospective study of these patients to determine their nature and duration.     

Synthesis and properties of oligodeoxynucleotides with an AP site at a preselected position.

A general synthesis of a deoxyoligonucleotide with an AP site at a preselected sequence is described. Deoxyuridine is introduced during routine oligonucleotide syntheses of d(TTTUTTTT) and d(AAAAGTTUAAAACAT). Treatment with uracil DNA-glycosylase produces d(TTTrTTTT), where r = deoxyribose, and d(AAAAGTTprpAAAACAT). KM and Vmax are: d(TTTUTTTT), 7.3 X 10(-9)M and 2.0 X 10(-9) mumol/min; d(AAAAGTTUAAAACAT), 1.5 X 10(-8) M and 6.4 X 10(-9) mumol/min. Both d(AAAAGTTprpAAAACAT) and d(TTTprpTTTT) undergo rapid beta-elimination in 1 M piperidine at 25 degrees giving two oligonucleotide fragments, d(AAAAGTTpr') and d(pAAAACAT), where r' = -O-CH2-CHOH-CH=CH-CHO (or its hemiacetal form). The fragment, d(AAAAGTTpr'), which can be isolated by reverse phase chromatography, is resistant to the 3'----5' exonuclease activity of snake venom phosphodiesterase. Endonucleolytic hydrolysis of the penultimate phosphodiester occurs removing pTpr' and generating a normal 3'-OH end. In 1 M piperidine at 90 degrees two beta-eliminations occur producing the oligonucleotides d(AAAAGTTp) and d(pAAAACAT) from d(AAAAGTTprpAAAACAT); d(TTTp) and d(pTTTT) from d(TTTprpTTTT).     

Value of measuring end tidal partial pressure of carbon dioxide as an adjunct to treadmill exercise testing

The end tidal partial pressure of carbon dioxide (Pco₂) was measured during treadmill exercise in 30 normal controls and 113 patients referred for assessment of chest pain. Among the 92 patients without significant ST depression hypocapnia occurred more often in those reporting “typical” than “atypical” chest pain (17 of 22 patients compared with 29 of 70; p<0·01). Hypocapnia was uncommon in patients with significant ST depression whether reporting typical or atypical chest pain (one of 10 patients and two of 11, respectively).Hypocapnia at rest (Pco₂ <4 kPa) occurred in 16 (14%) patients but in only one control. Hypocapnia occurred during or after exercise in only one control and three of the 21 patients with significant ST depression on exercise (group 1). The remaining 92 patients were divided into those with a history suggestive of hyperventilation (group 2; n=30) and those without (group 3; n=62). Hypocapnia developed significantly more often in both these groups (21 and 25 patients respectively) than in controls or patients with significant ST depression.An abnormal response of the Pco₂ to exercise provided objective data to support a clinical suspicion of chest pain induced by hyperventilation in 24 cases, suggested a cause for equivocal ST depression other than coronary stenosis in five patients, and led to the diagnosis of previously unsuspected respiratory disease in 14 patients.Measurement of end tidal Pco₂ gives additional valuable diagnostic information during the conventional treadmill exercise test in patients with both typical and atypical chest pain.     

In vivo effect of DNA repair on the transition frequency produced from a single O6-methyl- or O6-n-butyl-guanine in a T:G base pair

Summary We have previously reported some effects of DNA repair on the transition frequencies produced by an O⁶-methyl-guanine (MeG) or an O⁶-n-butyl-guanine (BuG) paired with C at the first position of the third codon in gene G of bacteriophage X174 form I'DNA (Chambers et al. 1985). We now report experiments in which the transition is produced from T:MeG or T:BuG, instead of C:MeG or C:BuG, located at this site. The site-modified DNAs were transfected into cells with normal DNA repair as well as into cells with repair defects (uvrA, uvrB, uvrC, recA, uvrArecA). The lysates were screened for phage carrying the expected transition using a characteristic change in phenotype. The data demonstrate that the transition frequency from T:BuG is low (0.3% of total phage progeny) in cells with normal repair (Escherichia coli AB1157) and increases 7-fold in uvrA cells (E. coli AB1886). A similar increase is seen in uvrB and uvrC cells (AB1885, AB1884). These data, like our previous data, indicate BuG is repaired primarily by excision. In contranst to this, the transition frequency from T:MeG is high (5±2%) in cells with normal repair. After induction of alkyl transfer repair in E. coli AB1157, the transition frequency goes up 5-fold. Compared with cells with normal repair, the transition frequency goes up 2-fold in uvrA, uvrB and uvrC cells; it goes up 1.5-fold in recA cells (E. coli AB2463). The data reinforce our earlier conclusion that MeG is repaired primarily by alkyl transfer, but the ABC excinuclease as well as RecA protein inhibit this repair process. Using the BuG data reported here and in our previous paper, we calculate that BuG pairs with a thymine residue 0.5%–0.62% of the time during replication in vivo, and that BuG markedly inhibits replication of the strand that contains it. Because of the complication introduced by alkyl transfer repair, similar calculations for MeG cannot be made from the current data.Abbreviations MeG and BuG O⁶-methyl-or O⁶-n-butyl-guanine moiety in X DNA (in each case, the plus strand nucleotide is specified first) - form I'DNA relaxed, covalently closed, circular, double-stranded DNA - Wt wild-type phenotype - Am amber phenotype - pfu plaque forming units - MNNG N-methyl-N'-nitro-N-nitrosoguanidine X mutants are named by designating the gene, the type of mutation (e.g. ms=missense), the codon number, the mutant codon and the new amino acid (where pertinent) in that order (e.g. XGam3) carries an amber in the third codon of gene G, and should not be confused with the classical am3 mutant used in the older literature to designate what is now known to be XEam7     

Histone modifications accompanying the onset of developmental commitment

In the sea urchin, Strongylocentrotus purpuratus, three cell types comprise the 16-cell stage embryo: micromeres, macromeres, and mesomeres. We have analyzed these three cell types for nuclear proteins that were synthesized during the earliest stages of embryonic development. The most striking differences in composition of newly synthesized proteins were found between the micromeres, which are the most committed cell type, and the macromeres and mesomeres. First, the micromeres lacked triply modified forms of histone H3; the levels of doubly modified forms of H3 were also greatly reduced. In contrast, micromeres were enriched in a band which migrated at the position of unmodified, unacetylated, histone H3 protein. Second, the overall distribution of H2A histone variants differed among the three cell types. Compared with macromeres and mesomeres, micromeres had a higher ratio of alpha-stage to cleavage-stage (CS) histone H2A; the micromere nuclei were depleted by 50 and 35%, respectively, in embryonically synthesized histone CS-H2A. Third, micromeres displayed different profiles of H1 histones. (a) They contained a cleavage-stage H1 histone which migrated faster than that of macromeres and mesomeres. This protein displays the electrophoretic behavior expected for a protein with reduced levels of posttranslational covalent modification. (b) Micromeres also had reduced levels of an H1 histone (designated H1 alpha a) band found in the alpha-H1 region of macromeres and mesomeres. These changes in chromatin modification correlate with the degree of commitment of cells in the developing embryo; they may reflect differing activities of the chromatin modifying enzymes in the various cell types at the 16-cell stage. Thus, the newly synthesized chromatin proteins of the individual blastomere types already differ in the developing sea urchin by the 16-cell stage. We suggest that variations in histone subtypes and in the levels of activity of chromatin modifying enzymes, e.g., acetylases and phosphorylases, could be involved in commitment and differentiation of different cell types.     

Sequence of the Structural Gene for Xanthine Dehydrogenase ( rosy Locus) in Drosophila melanogaster

We determined the nucleotide sequence of a 4.6-kb EcoRI fragment containing 70% of the rosy locus. In combination with information on the 5' sequence, the gene has been sequenced in entirety. rosy cDNAs have been isolated and intron/exon boundaries have been determined. We find an open reading frame which spans four exons and would encode a protein of 1335 amino acids. The molecular weight of the encoded protein (xanthine dehydrogenase), based on the amino acid translation, is 146,898 daltons which agrees well with earlier biophysical estimates. Characteristics of the protein are discussed.