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Biomedical subjects

D Johnson

Publications and source records attributed to D Johnson.

At least 523 records · Page 29Linked to original sources
PubMed1989

Immunogold localization of the NodC and NodA proteins of Rhizobium meliloti.

Monospecific, polyclonal antibodies to the nodC and nodA gene products of Rhizobium meliloti were used in combination with immunogold labeling and transmission electron microscopy to localize the NodC and NodA proteins in cultures of R. meliloti. Both NodC and NodA were detected in the cytoplasm and cell envelope in thin sections of free-living rhizobia treated with luteolin, a known inducer of nod gene expression; however, only NodC was detected on cell surfaces when immunolabeling was performed with intact induced cells. In view of biochemical data characterizing NodC as an outer membrane protein with a large extracellular domain, the pattern of immunolabeling on thin sections suggests that NodC is produced on free cytoplasmic ribosomes prior to assembly in the membrane. The pattern of NodA labeling on thin sections is consistent with biochemical data detecting NodA in both soluble and membrane fractions of NodA-overexpressing strains of R. meliloti.

Acyltransferases↗
PubMed1989

A moveable 5' splice site in adenine phosphoribosyltransferase genes of Drosophila species.

In two distantly related Drosophila species, the use of alternate 5' splice sites to process an intron in pre-mRNA from homologous adenine phosphoribosyltransferase (APRT)-encoding genes led to RNAs encoding nonfunctional peptides in addition to APRT. The production of aberrantly spliced transcripts as a normal feature of gene expression supports a general model of eucaryotic gene evolution through alternative splicing and moveable splice junctions.

Adenine Phosphoribosyltransferase↗
PubMed1989

Plasma polyenoic very-long-chain fatty acids in peroxisomal disease: biochemical discrimination of Zellweger's syndrome from other phenotypes.

The plasma of patients with inherited defects in peroxisomal biogenesis (ie, Zellweger's syndrome, infantile Refsum's disease, and neonatal adrenoleukodystrophy) shows evidence of a disturbance in the metabolism of saturated and monoenoic fatty acids with carbon chain lengths greater than 22 (VLCFA). Zellweger's syndrome plasma alone contains, in addition, increased amounts of a number of n-6 polyenoic VLCFA including 24:5, 26:5, 28:5, 30:5, and 30:6 fatty acids. These fatty acids facilitate the biochemical discrimination of Zellweger's syndrome from other related phenotypes.

Adrenoleukodystrophy↗
PubMed1989

Large intestinal capacity, retention times, and turnover rates of particulate ingesta associated with extensive large-colon resection in horses.

Fecal excretion of a particulate marker, ytterbium (Yb), was evaluated in 9 horses before surgery and 3 weeks, 3 months, and 6 months (4 trials) after sham-operation (group 1; n = 3) or extensive large colon resection (group 2; n = 6). Fecal excretion curves of total Yb excretion, loge Yb excretion, % Yb excretion, loge % Yb excretion, and cumulative % Yb excretion were evaluated, and kinetic analysis was performed on the loge Yb excretion curves to detect mixing pools and to calculate the fractional rate of particulate passage, turnover rate, and pool size. Calculations were performed to determined transit time, mean overall retention time, adjusted mean retention time, peak time, and disappearance time. Values were statistically analyzed to determine differences between groups and among trials (P less than 0.05). Group-2 horses had significantly shorter transit, peak, and mean overall retention times, compared with preoperative values and with values for group-1 horses. Two mixing pools were identified: a slower emptying pool of 5.7% hour-1 (k1) and a faster emptying pool of 12.3% hour-1 (k2). The rate of passage from the first pool (k1) was not altered by colon resection, and was interpreted as being most influenced by the cecum. In further support of this interpretation, the capacity of the k1 pool approximated the capacity of the cecum (17 L). The capacity of the k1 pool significantly expanded by 6 months in the resected horses. the rate of passage from the second pool (k2) significantly increased initially after colon resection (3 weeks and 3 months), but returned to preoperative values by 6 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Unsuspected infectious diseases and other medical diagnoses in the evaluation of internationally adopted children.

Seven simple screening tests--hepatitis B profile, urine culture for cytomegalovirus, Mantoux test for tuberculosis, stool examination for ova and parasites, VDRL, complete blood cell count, and vision and hearing screening--were used to evaluate 52 consecutive children at a pediatric clinic for international adoptees. In 63% of these children, unsuspected medical diagnoses were made by a combination of history, physical examination, and appropriate screening tests. When only those children previously examined by a physician in the United States were included in our analysis, the rate of unsuspected diagnosis remained high (67%). Omission of screening tests was the single most frequent cause of missed diagnoses, of which the majority were infectious diseases. More than 50% of our newly established diagnoses carried the potential for long-term sequelae without proper treatment. These data emphasize that internationally adopted children should receive a thorough screening evaluation for medical problems that may adversely affect their growth and development.

Adoption↗
PubMed1988

Comparative, multicenter studies of cefixime and amoxicillin in the treatment of respiratory tract infections.

A total of 560 patients were treated in two double-blind, randomized multicenter studies to compare the safety and efficacy of cefixime (400 mg administered once daily) and amoxicillin (250 or 500 mg administered three times daily) for the treatment of bacterial respiratory tract infections. Eighty percent of the 244 patients treated in the lower respiratory tract infections (LRTI) study had acute bronchitis. Streptococcus pneumoniae (13 percent), Haemophilus influenzae (28 percent), and Escherichia coli (10 percent) were the pathogens most frequently isolated from sputum in these patients. Among evaluable patients with positive bacterial culture results at baseline, a favorable clinical response (cured or improved) was obtained in 100 percent of the cefixime-treated patients (22 of 22) and in 96 percent of the amoxicillin-treated patients (23 of 24). Bacteriologic eradication rates were 100 percent and 83 percent for cefixime and amoxicillin, respectively. In the upper respiratory tract infections (URTI) study, 316 patients with pharyngitis (80 percent) or tonsillitis (14 percent) were treated. Group A, beta-hemolytic Streptococcus (69 percent) and H. influenzae (8 percent) were the pathogens most frequently isolated from the throat culture specimens of these patients. Favorable clinical results were obtained in 99 percent of the evaluable cefixime-treated group (n = 73) and in 98 percent of the amoxicillin-treated group (n = 66). The bacteriologic eradication rates were 93 percent and 100 percent, respectively. The adverse experiences reported during both studies were similar in nature and frequency to those reported for other beta-lactam antibiotics with the exception of a higher incidence of altered bowel movement (diarrhea and stool changes) with both drugs. These episodes usually resolved without remedial medication when the treatment was withdrawn. No significant adverse laboratory findings were observed. Results of these trials demonstrate that cefixime at a dosage of 400 mg once daily is an effective and safe oral antibiotic for the treatment of acute respiratory tract infections.

Amoxicillin↗
PubMed1988

A double-blind, multicenter, comparative study of the safety and efficacy of cefixime versus amoxicillin in the treatment of acute urinary tract infections in adult patients.

In this 31-site multicenter trial, 565 adult patients with urinary tract infections were randomly assigned to receive either a 10-day course of cefixime 400 mg once daily (n = 279) or amoxicillin 250 mg three times daily (n = 286). Although all patients were included in the safety analysis, only 93 (33 percent) cefixime-treated and 99 (35 percent) amoxicillin-treated patients were fully evaluable for the efficacy analysis. One week after therapy, the evaluable patients treated with cefixime demonstrated a 90 percent clinical cure rate and a 92 percent eradication rate of the baseline pathogen. This compared with an 83 percent clinical cure rate and an 84 percent bacterial eradication rate in the amoxicillin-treated group. The most frequently isolated pathogen was Escherichia coli (80 percent) followed by Proteus mirabilis (10 percent). One hundred thirty-seven (49 percent) of the 279 cefixime-treated and 126 (44 percent) of the 286 amoxicillin-treated patients reported at least one adverse experience during the study. Adverse reactions associated with cefixime were similar to those reported for other beta-lactam antibiotics. The most frequent adverse experiences reported by cefixime-treated patients were diarrhea (15 percent) and stool changes (12 percent). Headaches (11 percent) and diarrhea (9 percent) were the most frequently reported adverse reactions by the amoxicillin-treated patients. Eleven cefixime-treated patients (3.9 percent) and 10 amoxicillin-treated patients (3.5 percent) discontinued therapy because of adverse experiences. Results of this study demonstrate that a once-daily regimen of cefixime is as safe and effective as a three-times-daily regimen of amoxicillin in the treatment of acute urinary tract infections. Although the incidence of bowel changes was somewhat higher in the cefixime treatment group, these events usually resolved when therapy was discontinued.

Acute Disease↗
PubMed1988

The occurrence of polyenoic very long chain fatty acids with greater than 32 carbon atoms in molecular species of phosphatidylcholine in normal and peroxisome-deficient (Zellweger's syndrome) brain.

The n-6 tetra- and pentaenoic fatty acids with carbon chain lengths greater than 32 found in normal brain are located predominantly in a separable species of phosphatidylcholine. A similar phospholipid is found in increased amounts in the brain of peroxisome-deficient (Zellweger's syndrome) patients, but the fatty acid composition differs in that penta- and hexaenoic derivatives predominate. Our data strongly suggest that the polyenoic very long chain fatty acids are confined to the sn-1 position of the glycerol moiety, while the sn-2 position is enriched in saturated, monounsaturated and polyunsaturated fatty acids with less than 24 carbon atoms. It is postulated that these unusual molecular species of phosphatidylcholine may play some, as yet undefined, role in brain physiology.

Brain Chemistry↗
PubMed1988

[3H]-p-azidopuromycin photoaffinity labeling of Escherichia coli ribosomes: evidence for site-specific interaction at U-2504 and G-2502 in domain V of 23S ribosomal RNA.

Previously we (1) showed that [3H]-p-azidopuromycin was a functional puromycin analogue that, on photolysis in the presence of 70S ribosomes from Escherichia coli, photoincorporated site specifically into proteins L23, L18/22, and L15 [Nicholson, A.W., Hall, C.C., Strycharz, W.A., & Cooperman, B.S. (1982) Biochemistry 21, 3809-3817] and (2) used immunoelectron microscopy to localize the principal sites of p-azidopuromycin photoincorporation within the 50S subunit [Olson, H.M., Nicholson, A.W., Cooperman, B.S., & Glitz, D.G. (1985) J. Biol. Chem. 260, 10326-10331]. These studies are here continued by identification of the principal sites of [3H]-p-azidopuromycin photoincorporation into ribosomal RNA. The major portion of such photoincorporation, 72%, takes place into 23S rRNA. Analysis by hybridization of the photoaffinity-labeled rRNA to restriction enzyme fragments of plasmid pKK3535, which contains rrnB DNA, using a refinement of a recently developed methodology [Hall, C.C., Smith, J.E., & Cooperman, B.S. (1985) Biochemistry 24, 5702-5711], shows that the most prominent [3H]-p-azidopuromycin photoincorporation occurs within bases 2445-2668 in domain V [Noller, H.F. (1984) Annu. Rev. Biochem. 53, 119-162] of 23S rRNA. Photoincorporation into this region is site specific, as demonstrated by the decrease in photoincorporation of radioactivity when unlabeled puromycin is included in the photolysis solution. Significant site-specific photoincorporation also occurs within bases 489-681 in domain II of 23S RNA. Further localization, by the method of reverse transcriptase primer extension [Barta, A., Steiner, G., Brosius, J., Noller, H.F., & Kuechler, E. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3607-3611], provides evidence that U-2504 and G-2502 are the principal sites of p-azidopuromycin interaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1988

The role of mast cells in demyelination. 1. Myelin proteins are degraded by mast cell proteases and myelin basic protein and P2 can stimulate mast cell degranulation.

Incubation of bovine peripheral myelin with supernatants from degranulated rat serosal mast cells led to extensive loss of P0. Similarly, when myelinated axons prepared from guinea pig CNS were incubated with degranulation supernatants, a significant loss of basic protein (MBP) was observed. As cationic peptides can stimulate mast cell degranulation, rat serosal mast cells were incubated with MBP, and with P2. Degranulation was assayed by measurement of release of the granule enzyme beta-hexosaminidase and it was found that both MBP and P2 stimulated 40-50% degranulation at a concentration of 50 micrograms/ml. The results of this study suggest that release of mast cell proteases could contribute to myelin damage in both the PNS and CNS, and that subsequent release of P2 or MBP or their breakdown products could potentiate further mast cell degranulation.

Animals↗