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Biomedical subjects

H B Machado

Publications and source records attributed to H B Machado.

13 recordsLinked to original sources
PubMed2001

Potential roles for the glnB and ntrYX genes in Azospirillum brasilense.

Three Azospirillum brasilense mutants constitutive for nitrogen fixation (Nif(C)) in the presence of NH4(+) and deficient in nitrate-dependent growth were used as tools to define the roles of the glnB and ntrYX genes in this organism. Mutant HM14 was complemented for nitrate-dependent growth and NH4(+) regulation of nitrogenase by plasmid pL46 which contains the ntrYX genes of A. brasilense. Mutant HM26 was restored for NH4(+) regulation and nitrate-dependent growth by plasmid pJC1, carrying the A. brasilense glnB gene expressed from a constitutive promoter. Mutant HM053, on the other hand, was not complemented for NH4(+) regulation of nitrogenase and nitrate-dependent growth by both plasmids pJCI and pL46. The levels and control of glutamine synthetase activity of all mutants were not affected by both plasmids pL46 (ntrYX) and pJC1 (glnB). These results support the characterization of strains HM14 as an ntrYX mutant and strain HM26 as a glnB mutant and the involvement of ntrYX and glnB in the regulation of the general nitrogen metabolism in A. brasilense.

Ammonia↗
PubMed2000

Expression of the nifA gene of Herbaspirillum seropedicae: role of the NtrC and NifA binding sites and of the -24/-12 promoter element.

The nifA promoter of Herbaspirillum seropedicae contains potential NtrC, NifA and IHF binding sites together with a -12/-24 sigma(N)-dependent promoter. This region has now been investigated by deletion mutagenesis for the effect of NtrC and NifA on the expression of a nifA::lacZ fusion. A 5' end to the RNA was identified at position 641, 12 bp downstream from the -12/-24 promoter. Footprinting experiments showed that the G residues at positions -26 and -9 are hypermethylated, and that the region from -10 to +10 is partially melted under nitrogen-fixing conditions, confirming that this is the active nifA promoter. In H. seropedicae nifA expression from the sigma(N)-dependent promoter is repressed by fixed nitrogen but not by oxygen and is probably activated by the NtrC protein. NifA protein is apparently not essential for nifA expression but it can still bind the NifA upstream activating sequence.

Bacterial Proteins↗
PubMed1996

Cloning and sequencing of the nitrogenase structural genes nifHDK of Herbaspirillum seropedicae.

The nitrogenase structural genes (nifHDK) of the endophytic diazotroph Herbaspirillum seropedicae were isolated from a genomic bank by plate hybridization. Sequence analysis of the DNA showed a consensus promoter region upstream for the nifH gene containing a -24/-12 type promoter together with NifA- and integration host factor (IHF)- binding sites. The derived protein sequences of NifH, NifD and NifK contained conserved cysteine residues for binding iron-sulfur clusters and the iron-molybdenum cofactor. These protein sequences showed the strongest similarities to the nifHDK gene products of the symbiotic diazotroph Bradyrhizobium japonicum (93.5%, 91.3% and 83.3%, respectively), the plant-associated diazotroph Azospirillum brasilense (90.0%, 83.7% and 75.1%, respectively) and to Thiobacillus ferrooxidans (91.0%, 83.4% and 81.1%, respectively) of the same phylogenetic group of the protobacteria.

Amino Acid Sequence↗
PubMed1995

The ntrBC genes of Azospirillum brasilense are part of a nifR3-like-ntrB-ntrC operon and are negatively regulated.

A cosmid able to complement the Nif- and nitrate-dependent growth phenotypes of the Azospirillum brasilense mutant FP9 was isolated from a genomic library of the wild-type strain FP2. A 6-kb DNA region was sequenced and showed two open reading frames (ORFs) identified as the ntrB and ntrC genes. An ORF1 located upstream from the ntrB gene and coding for a 36-kDa polypeptide showed similarity to the nifR3 gene of Rhodobacter capsulatus and the ORF1 of Rhizobium leguminosarum, both located upstream from the ntrB gene in a complex operon. Two other unidentified ORFs (ORF5 and partial ORF4) coding for hydrophobic polypeptides were also observed. delta ORF1-ntrBC, ORF1, ntrB, and ntrC mutants obtained by recombination of suicide plasmids containing an insertion of a promoterless lacZ kanamycin cassette showed decreased nitrogenase activities and were unable to grow on nitrate as the sole N source. These phenotypes were restored by complementation with plasmids containing the ntrC gene. Analysis of lacZ transcriptional fusions suggested that the ORF1-ntrBC operon in Azospirillum brasilense is expressed from a promoter located upstream from the ORF1 and that it is negatively regulated by the ntrC gene product.

Amino Acid Sequence↗
PubMed1993

Cloning of a recA-like gene from the diazotroph Herbaspirillum seropedicae strain Z78.

A recombinant plasmid, pBMR5, carrying a recA-like gene of Herbaspirillum seropedicae, was isolated from a H. seropedicae genomic library by intergeneric complementation of Escherichia coli recA mutant strain HB101. Quantitative survival experiments showed that pBMR5 restored the ultraviolet radiation and methyl methanesulfonate resistances and recombinational proficiency of this strain. Hybridization studies showed that there is DNA sequence homology between the recA gene of E. coli K12 and that of H. seropedicae. Restriction sites for EcoRI, HindIII, BamHI, and Bg/II were found in the DNA insert derived from H. seropedicae in pBMR5. A Tn5 insertional mutant of pBMR5, called pBMR26.2, failed to restore recombination proficiency and methyl methanesulfonate and ultraviolet resistance to recA mutants of E. coli.

Cloning, Molecular↗
PubMed1989

Postexercise electrocardiographic and clinical changes in patients with sick sinus syndrome.

Forty patients with sick sinus syndrome, 15 women and 25 men with a mean age of 53.83 +/- 13.34 years, were studied using a maximal graded bicycle stress test. None of the patients were using a pacemaker or being treated with drugs that would interfere with the sinus node function; one patient had family myocardiopathy and eight suffered from essential hypertension. All patients, including those suffering from very marked bradycardia (less than 40 beats/min) responded to the increased effort with increased heart rate. The exercise test was stopped in 22 patients (55%) after the appearance of clinical signs and in 4 (10%) after ST-segment depression greater than 1 mm. Eight (20%) finished the stress test after reaching the maximal heart rate according to age, due to an increase in sinus rate. The exercise produced or increased extrasystoles in five patients (12.5%), but only one was forced to suspend the test. The Q-T interval, corrected for heart rate according to Bazett's formula (QTc), was measured on the resting ECG before the start of the test and on the ECG recorded immediately following the end of the exercise in all patients, except one with atrial fibrillation. In 24 patients (60%), a QTc mean increase of 0.040 +/- 0.022 sec was observed at the end of the stress test. Fourteen (35%) had the usual shortening due to the increase in heart rate. One patient showed no variation of the QTc. A lengthening of the QTc at the end of the exercise in more than half of the patients was the most intriguing electrocardiographic change.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1980

On deriving the electrocardiogram from vectoradiographic leads.

The issue of whether a traditional or scientifically based system for applying electrodes to the body for routine electrocardiography may be resolved by deriving the 12-lead ECG from the Frank XYZ signals. The result, the ECGD, is sufficiently close to the ECG for serial comparisons to be valid. Reducing data acquisition to the XYZ signals alone has several technical advantages. These have been realized with the introduction of a computer system employing the ECGD at a large general hospital. Plotting the lead vectors of the ECGD on Aitoff's projection of the sphere brings out important relationships between the leads, one to another, and to the spatial directions of the QRS and T vectors. Reversing the polarity of a VR enhances the sequential relationship between the limb leads; this is taken advantage of in an educational display generated by the computer.

Computers↗
PubMed1979

Standardization of electrocardiographic interpretive statements: a menu for word processing.

Standardization of electrocardiographic interpretive statements is a goal of various coding systems, but word processing has not usually been considered. A simple, easily memorized system for clinical electrocardiography has been developed and used for approximately 60 000 interpretations. It takes the form of a "menu", in which boxes stand for various interpretive statements; the boxes are identified by mnemonics and marked by the interpreter when appropriate. The results provide better standardization, significant decreases in the numbers of descriptive statements and words per interpretation and considerable saving in typing time. Acceptance by the interpreters has been good. Features of the system allow for word processing as part of a polarcardiography computing system.

Computers↗
PubMed1979

XYZ data interpreted by a 12-lead computer program using the derived electrocardiogram.

The 12-lead electrocardiogram (ECG) derived from the Frank xyz signals was compared with the conventional 12-lead ECG using the Telemed computer system. In 100 cases studied. Telemed's interpretations were essentially similar in 77, but substantially different in 23. In the 23 cases, interpretations of the derived tracings tended to be more accurate in 14 cases, and less accurate in four cases. In the diagnosis of infarction the probability that the interpretation of the derived tracing will be correct more often was 90%. The better performance may have been related to closer agreement with the vectorcardiogram (VCG). As a substitute for the conventional ECG, the derived ECG offers the prospect of a computerized system that is more practical and more versatile than most currently used systems.

Bundle-Branch Block↗
PubMed1978

Persistent atrial standstill with atrial inexcitability.

Electrophysiologic studies including His bundle recording, atrial, and ventricular stimulation, were performed in three symptomatic patients with persistent atrial standstill of unknown etiology. The rhythm was junctional in two cases and ventricular in one. In two cases, evidence suggestive of associated impairment of the His bundle conduction system was found. The atria were inexcitable at multiple sites and no retrograde conduction to the right atrium could be elicited by ventricular pacing. Follow-up in the three cases, respectively for 48, 42 and 12 months after pacemaker implantation, revealed no return of spontaneous atrial electrical activity.

Adult↗
PubMedDate not supplied

Systolic time intervals and heart sounds in left bundle branch block.

Systolic time intervals and heart sounds were studied in twenty patients with left bundle branch block. A definite cause for the organic heart disease was not ascertained. Abnormal duration of the electromechanical systole (Q-A2), due to a prolongation both of the preejection period (PEP) and of the Q-M1 intervals, was found to exist in all. Prolongation of Q-M1 was due to lengthening either of the electromechanical interval (EMI) or of the pre-isovolumetric contraction time (PICT). Isovolumetric contraction time (ICT) was prolonged in thirteen patients only. There was a good correlation between LVET/ICT ratio and the duration of ICT intervals. Six patients showed a first heart sound of normal intensity and duration. There was no correlation between the duration of the systolic time intervals and the characteristics of the first and second heart sounds.

Aged↗