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Biomedical subjects

G S Harris

Publications and source records attributed to G S Harris.

At least 19 recordsLinked to original sources
PubMed1992

Electrophoretic studies on the assembly of the nitrogenase molybdenum-iron protein from the Klebsiella pneumoniae nifD and nifK gene products.

The electrophoretic properties of the molybdenum-iron (MoFe) protein component of nitrogenase and an iron-molybdenum cofactor (FeMoco)-reactivatable apoMoFe protein from Klebsiella pneumoniae were examined under anaerobic ([O2] < 5 ppm), nondenaturing conditions. In wild type K. pneumoniae extracts, two immunoreactive species migrating more slowly than purified MoFe protein were detected using anti-MoFe protein antibodies. The uppermost species comigrates with the apoMoFe protein produced by a K. pneumoniae mutant unable to synthesize FeMoco (UN106) and by Escherichia coli harboring the plasmids pVL222+pVL15 (nifHDKTYUSWZM+A). In vitro FeMoco titration of the UN106 and pVL222+pVL15 extracts increases the electrophoretic mobility of the apoMoFe protein to that of purified MoFe protein in a two-step process giving rise to a species of intermediate mobility between the apo- and holoMoFe proteins. Two-dimensional gel electrophoresis showed that a 20-kDa peptide is associated with the apoMoFe protein and with the intermediate species, but not with the holoMoFe protein. N-terminal sequencing identified this associated peptide as the nifY gene product, which we propose is acting as a temporary enforcer of the apoMoFe protein structure required for cofactor binding that is released upon FeMoco activation. This FeMoco-induced mobility shift was used to characterize the mutant apoMoFe proteins produced in E. coli as a result of deleting the various nitrogen fixation (nif) genes from the plasmid pVL222. E. coli extracts bearing plasmids deleted in nifH, nifS, nifTYUM, or nifWZM exhibit less than 10% of the apoMoFe protein activity of derepressed UN106 and contain an immunoreactive species whose electrophoretic mobility is increased upon addition of FeMoco from that of apoMoFe protein to that of holoMoFe protein in a single step. Anaerobic nondenaturing gel electrophoresis of 55Fe-labeled E. coli extracts followed by autoradiography showed that these inactive apoMoFe species do not contain iron, indicating that the P-clusters are absent. We therefore propose that NifH, S, U, W, Z, and M are all involved, to varying degrees, in P-cluster assembly. In addition, the presence of the P-clusters does appear to be necessary for the two-step FeMoco activation of the apoMoFe protein to occur.

Amino Acid Sequence↗
PubMed1992

Cloning of a locus involved in Streptococcus mutans intracellular polysaccharide accumulation and virulence testing of an intracellular polysaccharide-deficient mutant.

The streptococcal transposon Tn916 (Tcr) was used to isolate mutants of Streptococcus mutans altered in glycogen accumulation to investigate whether glycogenlike intracellular polysaccharides (IPS) play an important role in S. mutans-induced caries formation. S. mutans UA130 (serotype c) was transformed with the Escherichia coli plasmid pAM620 (Tn916), and the resultant transposon libraries were screened for glycogen content by iodine staining. A transposon mutant, designated SMS201, demonstrated a glycogen-deficient phenotype on glucose-enriched medium. Quantitative electron microscopy confirmed that IPS concentrations were significantly reduced in SMS201 relative to the wild-type progenitor strain, UA130. Importantly, reversion to wild type correlated at all times with loss of the transposon. Transposon excisants were used to facilitate cloning of the streptococcal gene(s) involved in glycogen biosynthesis and storage. A 2.1-kb chromosomal determinant (glgR) which encodes a putative regulator of S. mutans glycogen accumulation was isolated. A stable deletion mutation (delta glgR) was subsequently generated in E. coli and introduced into S. mutans by allelic exchange. The resultant glycogen synthesis-deficient mutant, SMS203, demonstrated a significantly reduced cariogenic potential (P less than 0.01) on the buccal, sulcal, and proximal surfaces of teeth in germfree rats, relative to animals challenged with the glycogen synthesis-proficient progenitor strain, UA130. These observations confirm previous reports (J. M. Tanzer, M. L. Freedman, F. N. Woodiel, R. L. Eifert, and L. A. Rinehimer, p. 597-616, in H. M. Stiles, W. J. Loesche, and T. L. O'Brien, ed., Proceedings in Microbiology. Aspects of Dental Caries. Special Supplement to Microbiology Abstracts, vol. 3, 1976) which implicate IPS as significant contributors to the S. mutans cariogenic process.

Animals↗
PubMed1992

Choroidal detachment associated with retinal detachment as a presenting finding.

Choroidal detachment along with retinal detachment as a presenting finding is rare. We identified five such cases presenting to our ophthalmology practice between 1964 and 1991. The patient is usually myopic and presents with marked visual loss, profound hypotony and a marked anterior chamber reaction. The pathogenesis seems to revolve around the hypotony and myopia and an unstable choroidal vascular system. Management usually involves a scleral buckling procedure with cryotherapy under direct visualization to release choroidal and subretinal fluid, possibly preceded by a few days of anti-inflammatory therapy. The overall prognosis is poor owing to delays in diagnosis and the postoperative development of proliferative vitreoretinopathy.

Adult↗
PubMed1991

A comparative study of a progestin-only oral contraceptive versus non-hormonal methods in lactating women in Buenos Aires, Argentina.

A non-randomized comparative clinical trial of the progestin-only oral contraceptive (POC), Ovrette (75 mcg norgestrel) (Wyeth), versus non-hormonal methods was conducted at two clinics in Buenos Aires, Argentina. The trial was designed to assess the breast-feeding patterns of women choosing progestin-only oral contraception and non-hormonal methods of contraception, and to study the relationship between lactation and the clinical performance of a POC. Five-hundred women were allocated to either the progestin-only pill group (n = 250) or to the non-hormonal group (n = 250) and were followed up monthly for six months after admission. Measurements in mean infant weight, mean infant length, and mean head circumference were similar throughout the follow-up period. Non-hormonal users reported significantly more self-perceived decreases in milk production at the 5th and 6th month follow-up intervals. Acceptance and continued use of the pill were excellent, with only one woman discontinuing because of a pregnancy which was attributed to user failure. The principal side effect reported by women in both groups was intermenstrual bleeding.

Adolescent↗
PubMed1990

Genes required for formation of the apoMoFe protein of Klebsiella pneumoniae nitrogenase in Escherichia coli.

A binary plasmid system was used to produce nitrogenase components in Escherichia coli and subsequently to define a minimum set of nitrogen fixation (nif) genes required for the production of the iron-molybdenum cofactor (FeMoco) reactivatable apomolybdenum-iron (apoMoFe) protein of nitrogenase. The active MoFe protein is an alpha 2 beta 2 tetramer containing two FeMoco clusters and 4 Fe4S4 P centers (for review see, Orme-Johnson, W.H. (1985) Annu. Rev. Biophys. Biophys. Chem. 14, 419-459). The plasmid pVL15, carrying a tac-promoted nifA activator gene, was coharbored in E. coli with the plasmid pGH1 which contained nifHDKTYENXUSVWZMF' derived from the chromosome of the nitrogen fixing bacterium Klebsiella pneumoniae. The apoMoFe protein produced in E. coli by pGH1 + VL15 was identical to the apoprotein in derepressed cells of the nifB- mutant of K. pneumoniae (UN106) in its electrophoretic properties on nondenaturing polyacrylamide gels as well as in its ability to be activated by FeMoco. The constituent peptides migrated identically to those from purified MoFe protein during electrophoresis on denaturing gels. The concentrations of apoMoFe protein produced in nif-transformed strains of E. coli were greater than 50% of the levels of MoFe protein observed in derepressed wild-type K. pneumoniae. Systematic deletion of individual nif genes carried by pGH1 has established the requirements for the maximal production of the FeMoco-reactivatable apoMoFe protein to be the following gene products, NifHDKTYUSWZM+A. It appears that several of the genes (nifT, Y, U, W, and Z) are only required for maximal production of the apoMoFe protein, while others (nifH, D, K, and S) are absolutely required for synthesis of this protein in E. coli. One curious result is that the nifH gene product, the peptide of the Fe protein, but not active Fe protein itself, is required for formation of the apoMoFe protein. This suggests the possibility of a ternary complex of the NifH, D, and K peptides as the substrate for the processing to form the apoMoFe protein. We also find that nifM, the gene which processes the nifH protein into Fe protein (Howard, K.S., McLean, P.A., Hansen, F. B., Lemley, P.V., Kobla, K.S. & Orme-Johnson, W.H. (1986) J. Biol. Chem. 261, 772-778) can, under certain circumstances, partially replace other processing genes (i.e. nifTYU and/or WZ) although it is not essential for apoMoFe protein formation. It also appears that nifS and nifU, reported to play a role in Fe protein production in Azotobacter vinelandii, play no such role in K. pneumoniae, although these genes are involved in apoMoFe formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1989

Characterization of alpha and beta tubulin genes in the dimorphic fungus Histoplasma capsulatum.

Evidence from our laboratory indicates that microtubules are involved in the differentiation of the dimorphic, pathogenic fungus Histoplasma capsulatum; therefore, we cloned the tubulin genes from a virulent strain of the organism. We report that the H. capsulatum genome contains a single alpha (TUB1) and a single beta (TUB2) tubulin gene rather than the more typical multigene family which is common in even the simplest eukaryotes. Sequence data from these genes reveal a high degree of nucleotide and protein sequence conservation relative to tubulins from other species. The coding regions of TUB1 and TUB2 contain five and eight intervening sequences, respectively. Field inversion gel electrophoresis of H. capsulatum chromosome-sized DNA fragments indicates that the TUB1 and TUB2 genes are unlinked. Potential regulatory elements common to both genes have been identified in the 5' promoter regions. These elements may direct the coordinate expression of TUB1 and TUB2 during differentiation. The cloning and characterization of alpha and beta tubulin genes from H. capsulatum provides the first description of gene structure in this widely distributed pathogenic fungus. Isolation of the tubulin genes will facilitate future studies of tubulin gene expression during the dimorphic phase transitions and clarify the role of microtubules in the differentiation process.

Amino Acid Sequence↗
PubMed1989

Expression of alpha- and beta-tubulin genes during dimorphic-phase transitions of Histoplasma capsulatum.

Recent investigations have confirmed the presence of one alpha-tubulin gene (TUB1) and one beta-tubulin gene (TUB2) in the dimorphic fungus Histoplasma capsulatum. In the present study, Northern blot (RNA blot) analyses revealed multiple alpha-tubulin transcripts and a single beta-tubulin transcript in the yeast and mycelial phases of the high-virulence 217B strain and low-virulence Downs strain. S1 nuclease protection assays demonstrated one initiation start site and two major stop sites for the TUB1 transcripts, suggesting that variations in 3' processing generate the alpha-tubulin messages of 2.5 and 2.0 kilobases. Dot blot hybridization experiments indicated that tubulin gene expression is developmentally regulated during the dimorphic phase transitions. alpha- and beta-tubulin mRNAs increased six- to eightfold during the yeast-to-mycelium conversion and decreased two- to threefold during the reverse transition. These changes in tubulin mRNA content coincided with major morphological events associated with H. capsulatum development. Western blots (immunoblots) of H. capsulatum yeast-specific proteins resolved by two-dimensional gel electrophoresis demonstrated a single alpha- and a single beta-tubulin isoform. Multiple tubulin polypeptides expressed in mycelia are probably products of posttranslational modifications.

Endonucleases↗
PubMed1986

Pseudomonas aeruginosa and cystic fibrosis: unusual bacterial adaptation and pathogenesis.

Pseudomonas aeruginosa is an adaptable, saprophytic bacterium with the potential to cause a variety of opportunistic infections in compromised hosts. In patients with cystic fibrosis, chronic pulmonary colonization with mucoid alginate-producing mutants of P. aeruginosa is a major cause of morbidity and mortality and is an interesting example of microbial adaptation and host-bacterium interaction.

Adaptation, Physiological↗
PubMed1985

An examination of the prepatent period and the absence of a crowding effect in Angiostrongylus cantonensis in laboratory rats.

The effects of the size of the infective inoculum on the prepatent period and the effect of crowding on body volume were examined in populations of Angiostrongylus cantonensis (Metastrongyloidea: Angiostrongylidae) in the laboratory rat. Groups of five rats were infected with 5, 10, 20 and 40 L3 of A. cantonensis, respectively. The prepatent period was determined by examination of faeces using a modified Baermann technique. The prepatent period ranged from 37 to 45 days and was best described by a negative logarithmic curve (y = 51.21 + x-3.838). Based on developmental data in the literature, it is suggested that 37 days represents the minimum prepatent period for A. cantonensis in this host. Worm population showed a significant, positive increase with inoculum size, yet there was no relationship between worm volume and population size in females and a slight, but significant, increase in worm volume and population size in males from rats necropsied 76-84 days post-infection. It is concluded that crowding is likely to have little effect on worm size in rats naturally infected with A. cantonensis.

Angiostrongylus↗
PubMed1984

Assessment of anti-streptokinase antibody levels in human sera using a microradioimmunoassay procedure.

A high capacity, quantitative radioimmunoassay procedure has been developed to measure IgG antibodies to streptokinase (SK) in human serum. Results showed that the use of low concentrations of 125I-SK (100 ng/ml) and ambient temperature incubation conditions minimised degradation of the target labelled antigen and afforded antibody binding values which could be confidently related to the native intact SK protein. SK-complexed to plasminogen was also shown to retain the equivalent antigenic activity of native SK. Comparison of the absolute anti-SK levels with streptokinase resistance titres demonstrated that the two measurements of antibody correlated statistically but afforded quantitatively poor agreements. A survey of IgG levels to SK in sera from 93 normal healthy volunteers showed that all individuals displayed readily measurable anti-SK antibodies, with some 80% having IgG concentration capable of binding in excess of 1 microgram SK per ml serum.

Antibodies↗
PubMed1984

Comparison of the hypotensive effects of streptokinase-(human) plasmin activator complex and BRL 26921 (p-anisoylated streptokinase-plasminogen activator complex) in the dog after high dose, bolus administration.

In view of current interest in the possibility of rapid, high-dose administration of thrombolytic agents by the intravenous route in patients with coronary thrombosis (AMI), a study of this technique was carried out in the dog. Streptokinase-(human) plasmin activator complex (SK-Pm) and BRL 26921 (p-anisoylated streptokinase-(human) plasminogen activator complex) were each given at equivalent doses (28,500 IU/kg and 800 micrograms/kg respectively) to groups of beagle dogs by rapid injection over 10 sec and their effects on blood pressure, plasmin formation and kallikrein production were compared over the next 3h. SK-Pm produced, within 1-3 min, a pronounced hypotensive effect that was kinetically related to a rapid and steep rise in systemic plasmin and kallikrein concentrations. BRL 26921 had no hypotensive effect, the rise in plasmin production was slower and the rate and extent of kallikrein formation was significantly less than in the SK-Pm group.

Animals↗
PubMed1984

Choroidal osteomas.

Two cases of choroidal osteoma (one bilateral) are reported, bringing the total number of cases in the English-language literature to 18; an additional 7 cases are known to the authors. This tumour, first described in 1978, arises in the inner third of the juxtapapillary choroid and consists of mature bone; it is likely an osseous choristoma. It transmits light in an unusual manner, small lacunae glowing with sclerotic scatter. If the bony plaque is peripheral its solid nature can be identified with scleral depression. Computerized tomography readily demonstrates the calcification and the pattern of bone density.

Adult↗
PubMed1982

Management of infective endophthalmitis by pars plana vitrectomy.

Endophthalmitis is an ocular disaster that frequently leads to blindness. With the advent of vitrectomy and the opportunity for intraocular injection of antibiotics more of the eyes can be salvaged. In 11 patients the infection was controlled by vitrectomy. All had dramatic relief of pain, and eight showed an improvement in visual acuity. Pathogens were cultured from the aqueous or the vitreous, or both, of 64%, and from the conjunctival swabs of the remainder.

Adult↗
PubMed1981

A randomized prospective study of the use-effectiveness of two methods of natural family planning.

The final results of a prospective comparative study of two methods of natural family planning indicate a significant difference in the 12 month net cumulative pregnancy rates between the ovulation and symptothermal methods. These differences are on the order of two to one in favor of the symptothermal method. Pearl pregnancy rates confirm similar differentials between the two methods. Dropout rates for both methods were high. Lack of interest or dissatisfaction with the method was the major reason for dropout training while pregnancy or desire for pregnancy were the major reasons for dropout during the formal phase of the study.

Adult↗
PubMed1979

A randomized prospective study of the use-effectiveness of two methods of natural family planning: an interim report.

Data accumulated to date from the Los Angeles study indicate that the total termination rate for 12 months from the beginning of the training period and from formal entry into the study was high for the ovulation method (OM), and symptothermal method (STM). Voluntary withdrawal was the highest single reason for termination in both methods. The 12 month voluntary withdrawal rate, measured from formal entry into the study, was significantly higher for OM users. Pregnancy rates measured from both the beginning of training and formal entry into the study were significantly higher for OM users than for STM users. Complete analysis of the data collected during the study is currently in progress. It is anticipated that some of the causes for the differences in pregnancy rates and withdrawal rates between the two methods can be identified.

Adult↗
PubMed1977

The prophylactic treatment of retrolental fibroplasia.

10 premature infants with stage 3 retinopathy of prematurity have had photocoagulation and/or cryocoagulation therapy to one eye and have been followed for a period of 1-6 years. Although the long-term results of this therapy are not known, particularly in the prevention of retinal detachment, early observations suggest that treatment is neither harmful nor particularly beneficial. Macular dragging does not seem to be influenced by treatment. The refractive error, as one would expect, does not appear to be altered by this form of therapy. Marked amelioration of the vascular dilatation and tortuosity at the posterior pole is apparent shortly after treatment. It is stressed that this is a trial project and until more definite beneficial results are obtained, treatment of stage 3 retinopathy should be deferred. Retinal detachments (stage 4) may be quite amenable to a buckling procedure.

Child↗
PubMed1976

Visual field changes in branch retinal 'vein' occlusion.

The visual field defects in 20 consecutive patients who had branch retinal "vein" occlusions included arcuate nerve fiber bundle scotomas, central scotomas, paracentral scotomas, and segmental peripheral constriction. The role of retinal arteriolar insufficiency in the production of these field defects is discussed. The available evidence suggests that the term "branch retinal vascular occlusion" is a preferable term to describe such clinical findings.

Adult↗