Palaeoanthropology. Second gorilla or third chimp?
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Animals↗
Biomedical subjects
D Dean
Publications and source records attributed to D Dean.
Ionic interactions in the nitrogenase complex. Properties of Fe-protein containing substitutions for Arg-100.
A series of Azotobacter vinelandii strains have been constructed in which the nitrogenase Fe-protein (Av2) was altered by substitutions for Arg-100. This invariant residue is a likely partner in a salt bridge with the MoFe-protein and, in some species, is the site of reversible regulation by ADP-ribosylation (Pope, M. R., Murrell, S. A., and Ludden, P. W. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 3173-3177). Although we find that arginine is the optimum amino acid, other residues in this position could support diazotrophic growth. These results were surprising because Klebsiella pneumoniae Fe-protein substituted by His-100 had been reported to be inactive (Lowery, R. G., Chang, C. L., Davis, L. C., McKenna, M.-C., Stevens, P. J., and Ludden, P. W. (1989) Biochemistry 28, 1206-1212). Two altered Fe-proteins (Av2-R100Y, the tyrosyl form, and Av2-R100H, the histidyl form) were isolated and, in contrast to this earlier report, we found that both had some activity in acetylene reduction. However, both altered proteins exhibited a decreased maximum velocity (35 and 3% of wild type, respectively) and were strongly inhibited by excess MoFe-protein. These adverse activity parameters were also manifest in the increased sensitivity of the altered proteins to inhibition by salts. Indeed, the salt sensitivity of Av2-R100H is so significant that its activity is masked in the normal assay and is easily missed. In addition, for Av2-R100H, substrate reduction is substantially uncoupled from MgATP hydrolysis. These results suggest that substitutions for Arg-100 may decrease the affinity of the Fe-protein for the MoFe-protein prior to electron transfer but increase affinity after electron transfer. Hence, the role of Arg-100 may be to provide the optimum balance in stabilities of these two complexes for maximum efficiency in substrate reduction.
Acetylene↗
The nifU, nifS and nifV gene products are required for activity of all three nitrogenases of Azotobacter vinelandii.
Strains with mutations in 23 of the 30 genes and open reading frames in the major nif gene cluster of A. vinelandii were tested for ability to grow on N-free medium with molybdenum (Nif phenotype), with vanadium (Vnf phenotype), or with neither metal present (Anf phenotype). As reported previously, nifE, nifN, nifU, nifS and nifV mutants were Nif- (failed to grow on molybdenum) while nifM mutants were Nif-, Vnf- and Anf-. nifV, nifS, and nifU mutants were found to be unable to grow on medium with or without vanadium, i.e. were Vnf- Anf-. Therefore neither vnf nor anf analogoues of nifU, nifS, nifV or nifM are expected to be present in A. vinelandii.
Azotobacter vinelandii↗
Comparison of the major outer membrane protein variant sequence regions of B/Ba isolates: a molecular epidemiologic approach to Chlamydia trachomatis infections.
The molecular evaluation of the chlamydial major outer membrane protein (MOMP) gene (omp1) can facilitate epidemiologic investigations of this pathogen. Genotyping of omp1 provides a more precise characterization of Chlamydia trachomatis than do current immunotyping techniques. Genetic omp1 variants of serovars that are responsible for ocular disease in Tunisia were identified. Archival conjunctival samples collected during 1972 and 1975 from trachoma patients in Douz were sequenced by automation along with additional B and Ba trachoma and genital isolates. Over 90% of the nucleotide changes resulted in an amino acid substitution. Different amino acid sequence changes in variable segments 1, 2, and 4 were found in the specimens collected in 1975 from those collected in 1972. Determination of omp1 genotypes responsible for trachoma will be useful for prospective, epidemiologic studies to identify chlamydial reservoirs within the host, evaluate transmission patterns, and determine the antigenic variation of MOMP for rational vaccine development.
Amino Acid Sequence↗
Scarring alopecia in discoid lupus erythematosus.
The clinicopathological features of the scarring alopecia of discoid lupus erythematosus (DLE) were studied. Scarring alopecia was present in 34% of 89 patients with DLE and was associated with a prolonged disease course. More than half these patients had scalp involvement at the onset of the disease. There was a significant reduction in size of sebaceous glands in affected scalp. Perifollicular lymphocytic inflammation was maximal around the mid-follicle at the level of the sebaceous gland, which seems to be an important functional level in the follicle. There are changes in the expression of the matrix molecules, the proteoglycans, in the connective tissue sheath and the keratin intermediate filaments in the outer root sheath cells at this level in normal scalp and in diseased scalp. Loss of a population of mid-follicular stem cells may be important in the pathogenesis of scarring alopecia in DLE.
Adolescent↗
Absence of expression of class II major histocompatibility complex determinants on keratinocytes in bullous pemphigoid.
Aberrant expression of class II products of the major histocompatibility complex (HLA-D locus antigens) occurs on keratinocytes in several inflammatory dermatoses and on thyroid epithelial cells in autoimmune thyroiditis. The functional significance of aberrant HLA-D expression is unclear but it has been hypothesized that epithelial cells bearing these determinants may act as antigen-presenting cells for autoantigens. The aim of the present study was to investigate the pathogenesis of bullous pemphigoid using immunohistochemical methods to determine whether the HLA-D locus antigens are aberrantly expressed on keratinocytes in lesional and uninvolved skin. A panel of monoclonal antibodies to each of the HLA-D subregions (DR, DP and DQ) and to Langerhans cells was used. Epidermal expression of the HLA-D locus antigens was similar in patients and controls, and there was no significant increase in expression in lesional skin compared with uninvolved skin in six out of nine patients. In three out of nine patients slight enhancement of epidermal HLA-D expression in lesional epidermis corresponded to increased Langerhans cells rather than expression on keratinocytes. HLA-D locus antigens are absent from keratinocytes in bullous pemphigoid skin and aberrant expression of these determinants cannot therefore be implicated in antigen presentation.
HLA-D Antigens↗
Pemphigus and the terminal hair follicle.
The scalp is frequently involved in the autoimmune skin disease pemphigus. This study demonstrates the distribution of pemphigus antigen in the scalp terminal hair follicle; as well as being found in the epidermis, it is distributed throughout the whole hair follicle outer root sheath and in the dermal bulb matrix cells. The increase in volume of target antigen offered by the follicular epithelium could be a factor determining scalp involvement in pemphigus.
Adult↗
Direct sequence evaluation of the major outer membrane protein gene variant regions of Chlamydia trachomatis subtypes D', I', and L2'.
The nucleotide sequences of variable segments (VS) 1, 2, and 4 for the major outer membrane protein gene (omp1) of Chlamydia trachomatis were determined for serologically defined subtypes D', I', and L2'. Asymmetric DNA amplification was used to produce single-stranded DNA for direct sequencing. Amino acid substitutions were detected in VS1, VS2, and VS4 for I', in VS2 for L2', and in VS4 for D'. DNA sequencing of omp1 variant regions may be an important method for evaluating the molecular epidemiology of Chlamydia spp.
Amino Acid Sequence↗
Monte-Carlo simulation of multisite echinomycin-DNA interactions detected by in vitro transcription analysis.
The interaction of echinomycin with DNA was analyzed at 37 degrees C by in vitro transcription analysis using a 497 bp fragment of DNA containing the lac UV5 promoter. Sixteen discrete drug binding sites were detected. The mole fraction of blocked transcript at each site was monitored over 4 h, and the kinetic profile was analyzed by Monte-Carlo simulation. The time course for all 16 sites was fully described by this process. For each drug site, three parameters were resolved with the following variation between sites: relative drug occupancy (1-26), dissociation rate constant (0.06-0.70 min-1), and probability of termination of transcription (0-48%). Eight low-occupancy binding sites were at 5'-CA sequences (relative occupancy of 1.0-2.9). The eight major sites were all at 5'-CG sequences (relative occupancy of 6.3-26) and exhibited an average occupancy some 13-fold greater than the CA sites, corresponding to an average additional stability of approximately 1.6 kcal. The dissociation rates from apparent high-affinity sites were only partially correlated with relative occupancy. Ten binding sites exhibited a 3-48% probability of termination of transcription immediately adjacent to the 5'-CG central sequence. Termination probably arises from distortion of the DNA helix in regions flanking the binding site and was most dramatic (48% probability) where two adjacent CG sites were separated by only 1 bp. This termination phenomenon may well account for the observed effects of echinomycin in vivo.
Base Sequence↗
Serious poisonings among older adults: a study of hospitalization and mortality rates in Massachusetts 1983-85.
We analyzed poisoning-related hospitalization and mortality rates among older adults living in Massachusetts during 1983-85. While poisoning-related hospitalization rates of individuals greater than or equal to 60 years were near the state average, death rates for men greater than or equal to 70 years and for women over 60 were higher than those of younger individuals. Medications and carbon monoxide were commonly implicated agents in these poisoning deaths. Older adults are more vulnerable to death from a poisoning than are younger age groups.
Aged↗
Biogenesis of molybdenum cofactors.
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Biological Transport↗
New insight into drug-DNA interactions at individual drug binding sites probed by RNA polymerase during active transcription of the DNA.
An in vitro transcription assay has been used to probe drug-DNA interactions during active transcription of the DNA. The method relies upon the formation of a stable, synchronized population of initiated transcripts comprising a short length of RNA, achieved by the absence of one nucleotide in the initiation mixture. Subsequent equilibration of the transcription complex with drug, followed by elongation of the initiated transcripts, yields lengths of RNA determined by transcription up to each drug-occupied site. A variety of site-specific phenomena have been observed, including delayed termination of transcription 5-10 bp downstream of actinomycin binding sites; 10-20% probability of termination at most echinomycin sites; drug residence-time-dependent termination of bacteriophage polymerases; enhanced residence time compared to physicochemical measurement of drug-DNA dissociation rates. The use of two counter-directed promoters separated by 100 bp results in a sensitive bidirectional transcription footprinting procedure able to resolve adjacent drug sites separated by only 1 bp. The significance of the method of in vitro transcription is the ability to quantitate a range of parameters describing individual drug sites in situations where multiple drug-DNA interactions exist.
Base Sequence↗
Case report. Guided tissue regeneration II.
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Adult↗
Fe:S cluster ligands are the only cysteines required for nitrogenase Fe-protein activities.
Serine substitutions for the five conserved cysteins (residues 38, 85, 97, 132, and 184) have been made in the Azotobacter vinelandii nitrogenase Fe-protein by site-specific mutagenesis. At least moderate levels of enzyme activity (greater than 10% of wild type enzyme) were found for enzymes with serine substitutions at residues 38, 85, and 184; whereas, no activity was detected for enzymes with serines at residues 97 and 132. This is consistent with cysteines 97 and 132 being the four ligands to the Fe:S cluster (two ligands from each of the two identical subunits). Although previous chemical modification studies had implicated these residues as ligands, the earlier results did not portend the new finding that of all the conserved cysteines only these 2 residues are required for a second function of the Fe-protein. Namely, if either cysteine 97 or 132 is replaced, it appears that a functional Fe:S cluster cannot be incorporated into the apo-Fe-protein. The consequence is that these altered Fe-proteins cannot participate either in substrate reduction or in the biosynthesis of FeMo-cofactor, a metallocofactor of the MoFe-protein. These results implicate the Fe:S center of Fe-protein in the biosynthesis mechanism as either a redox partner or Fe:S donor. Additional results suggest that the posttranslational modification of Fe-protein by nifM product is not the insertion of the Fe:S center.
Adenosine Triphosphate↗
Putting patients first.
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Delivery of Health Care↗