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Biomedical subjects

J W Thomas

Publications and source records attributed to J W Thomas.

At least 19 recordsLinked to original sources
PubMed1992

The low-spin heme site of cytochrome o from Escherichia coli is promiscuous with respect to heme type.

Cytochrome o of Escherichia coli is able to incorporate two different structures of heme, either heme B (protoheme) or heme O, in its low-spin heme site. In contrast, the heme of the binuclear O2 reduction site is invariably heme O. Heme O is a newly discovered heme that is related to heme A, but with the formyl group of the latter replaced by methyl. Enzyme isolated from wild type E. coli has predominantly heme B in the low-spin site, whereas enzyme isolated from various overexpressing strains contains both types of enzyme in different proportions. In some strains, 70% of the enzyme has heme O in the low-spin site. Despite this variation in the structure of one of the prosthetic groups, the enzymatic activity and polypeptide composition of the enzyme remain virtually constant. EPR and activity data both indicate that heme B and heme O occupy the same low-spin heme site in the enzyme. With heme O in this site, the alpha-absorption band is narrower and further to the blue, and the Em,7 is lower, than when there is heme B in the site. In contrast to previous proposals, we show here that the enzyme does not exhibit significant spectral interactions between the hemes. The structural heterogeneity of the low-spin heme accounts for the variation in the optical spectra and redox properties of the enzyme as isolated from different strains of E. coli.

Binding Sites↗
PubMed1992

Determination of the ligands of the low spin heme of the cytochrome o ubiquinol oxidase complex using site-directed mutagenesis.

The cytochrome o complex of Escherichia coli is a ubiquinol oxidase which is the predominant respiratory terminal oxidase when the bacteria are grown under high oxygen tension. The amino acid sequences of three of the subunits of this quinol oxidase reveal a substantial relationship to the aa3-type cytochrome c oxidases. The two cytochrome components (b563.5 and o) and the single copper (CuB) present in the E. coli quinol oxidase appear to be equivalent to cytochrome a, cytochrome a3, and CuB of the aa3-type cytochrome c oxidases, respectively. These three prosthetic groups are all located within subunit I of the oxidase. Sequence alignments indicate only six totally conserved histidine residues among all known sequences of subunit I of the cytochrome c oxidases of various species plus the E. coli quinol oxidase. Site-directed mutagenesis has been used to change each of these totally conserved histidines with the presumption that two of these six must ligate to the low spin cytochrome center of the E. coli oxidase. The presence of the low spin cytochrome b563.5 component of the oxidase can be evaluated both by visible absorbance properties and by its EPR spectrum. The results unambiguously indicate that His-106 and His-421 are the ligands of the six-coordinate low spin cytochrome b563.5. Although the data are not definitive in making additional metal ligation assignments of the remaining four totally conserved histidines, a reasonable model is suggested for the structure of the catalytic core of the cytochrome o complex and, by extrapolation, of cytochrome c oxidase.

Amino Acid Sequence↗
PubMed1992

Anti-insulin and regulatory anti-idiotypic antibodies use the same germ-line VHIX gene.

In humans and in BALB/c mice, immune responses to the hormone insulin use evolutionarily related VHV (human) and VHIX (murine) gene families. To determine if these structural relationships include regulatory elements, BALB/c mice were pretreated with autologous immunoglobulin G (IgG) monoclonal antibodies (mAb) that recognize shared idiotopes on human anti-insulin antibodies and the subsequent immune response to human insulin assessed. One mAb, Id227, was found to augment and accelerate the insulin response by inducing a human idiotype that is expressed on both insulin-binding and non-insulin-binding BALB/c antibodies. Analysis of VH gene utilization by Id227 shows that it expresses a VHIX gene similar to that of anti-insulin mAb 125, but the anti-Id has no anti-insulin activity. Using DNA amplification, four germ-line VHIX genes were isolated from BALB/c liver DNA and sequence analysis shows that the anti-insulin and anti-Id are derived from the same germ-line gene. Consistent with its role as a regulatory idiotype, IgG Id227 entirely preserves germ-line sequence in the complementary determining regions and contains only three mutations in framework regions. These studies show that both structural and regulatory features of immune responses to conserved self antigens extend beyond species boundaries.

Amino Acid Sequence↗
PubMed1992

Retinal hemangioblastoma. A histologic, immunohistochemical, and ultrastructural evaluation.

The authors evaluated the histologic, immunohistochemical, and ultrastructural characteristics of two eyes with retinal hemangioblastoma from patients with von Hippel-Lindau and von Hippel disease. Results of histologic evaluation showed the eyes to have degenerative changes and residual retinal hemangioblastoma. Immunohistochemical stains performed for MAC-387, factor XIIIa, lysozyme, alpha 1 anti-chymotrypsin (histiocyte markers), factor VIII-associated antigen, ulex europeaus (endothelial markers), neuron-specific enolase, chromogranin, neurofilament (neuroectodermal/neural/neuroendocrine markers) and glial fibrillary acid protein (glial marker) showed normal retinal vascular endothelium, neurons, and glial cells to stain where expected. Vascular endothelium in the retinal hemangioblastomas stained for factor VIII and ulex europeaus. Interstitial cells in the stroma of the tumors failed to stain for the histiocyte markers, chromogranin, and neurofilament. The stromal cells stained for glial fibrillary acid protein and neuron specific enolase. Ultrastructural findings in both eyes included endothelial/pericyte-lined vascular channels, elongated stromal cells, and plump, vacuolated stromal cells with ultrastructural features consistent with glial cells. This study supports the concept that retinal hemangioblastoma is composed of a proliferation of capillaries and glial cells.

Adolescent↗
PubMed1992

Medical students' knowledge and misconceptions about aging: responses to Palmore's Facts on Aging Quizzes.

Palmore's Facts on Aging Quizzes I and II and Facts on Aging Mental Health Quiz were administered as a single test to third-year medical students before and after their 6-week Community Health and Family Medicine clerkship. The clerkship experience contributed to a small improvement in students' knowledge about the aged, net bias scores decreased from pre- to posttest, and scores on FAQI were significantly higher than scores on FAQII both pre- and posttest.

Aged↗
PubMed1992

HMO marketing and selection bias: are TEFRA HMOs skimming?

The research evidence indicates that health maintenance organizations (HMOs) participating in the Tax Equity and Fiscal Responsibility Act of 1982 (TEFRA) At-Risk Program tend to experience favorable selection. Although favorable selection might result from patient decisions, a common conjecture is that it can be induced by HMOs through their marketing activities. The purpose of this study is to examine the relationship between HMO marketing strategies and selection bias in TEFRA At-Risk HMOs. A purposive sample of 22 HMOs that were actively marketing their TEFRA programs was selected and data on organizational characteristics, market area characteristics, and HMO marketing decisions were collected. To measure selection bias in these HMOs, the functional health status of approximately 300 enrollees in each HMO was compared to that of 300 non-enrolling beneficiaries in the same area. Three dependent variables, reflecting selection bias at the mean, the low health tail, and the high health tail of the health status distribution were created. Weighted least squares regressions were then used to identify relationships between marketing elements and selection bias. Subject to the statistical limitations of the study, our conclusion is that it is doubtful that HMO marketing decisions are responsible for the prevalence of favorable selection in HMO enrollment. It also appears unlikely that HMOs were differentially targeting healthy and unhealthy segments of the Medicare market.

Advertising↗
PubMed1991

Selection bias in TEFRA at-risk HMOs.

The issue of selection bias was investigated using data from 22 HMOs who are enrolling Medicare beneficiaries under Tax Equity and Fiscal Responsibility Act of 1982 (TEFRA) at-risk contracts. The study differs from previously published analyses of this issue in that it deals with the current Medicare risk program (TEFRA) rather than with earlier Demonstration Programs; as an indicator of selection bias, it utilizes beneficiary functional health status at enrollment; and it examines selection not only at the mean of the health status distribution, but at the two tails (very disabled, very able) as well. For each of the participating HMOs, the functional health status of recent Medicare enrollees was compared with that of a control group of randomly chosen fee-for-service beneficiaries. None of the HMOs experienced adverse selection, whether measured in terms of overall (mean) health status of enrollees or in terms of the proportion of the very disabled population that chose to join. Nine of the 22 HMOs were considered to have experienced favorable selection on the basis of the mean health status of new enrollees. In addition, ten more HMOs were found to have experienced favorable selection in one or both tails of the health status distribution. Although a specific cause for the observed enrollment patterns is not identified, speculation is made on factors that may or may not contribute. Evidence suggests that beneficiary self-selection is probably a more important explanation of these patterns than purposeful actions of HMOs to discourage enrollment by sicker beneficiaries (i.e., "skimming").

Aged↗
PubMed1991

Investigating early readmission as an indicator for quality of care studies.

Readmission to a hospital shortly following a previous discharge may be viewed as an adverse outcome of care. Consequently, early readmission represents a potentially useful indicator for monitoring quality. While a number of recent research studies have focused on this issue, several important questions concerning appropriate use of early readmission as a quality of care indicator remain to be addressed. In this article, using data on all discharges for 1 year from 18 hospitals, several of these questions are investigated. Specifically, whether the significant predictors of readmission risk are different for different types of cases (defined using DRGs), whether case severity is an important predictor of readmission risk, whether readmission risks differ systematically with hospital size and other characteristics, whether readmission risk is a function of patients' lengths-of-stay, and whether readmission risk is influenced by whether or not patients are discharged home or into organized care environments are explored. For this study, the focus is on patients who experienced unplanned readmissions to acute care hospitals within 31 days of a prior discharge. The Patient Management Category classification system and ICD-9-CM diagnosis and procedure codes are used to identify, and then exclude from consideration, those readmissions that occurred as part of an appropriately planned sequence of care. In each of 22 sets of related DRGs, analysis of unplanned readmissions indicates that severity/complexity is an important risk factor for early readmission and that clinical and other risk factors differ for different DRG groups. Thus, in future studies of early readmissions, researchers will need to control for both the type (e.g., DRG) and severity/complexity of individual cases. In examining relationships between early readmission and hospital characteristics, no consistent patterns suggestive of quality of care problems were detected.

Age Factors↗
PubMed1991

Responses by lactating cows in commercial dairy herds to recombinant bovine somatotropin.

Cows (890) in 15 US herds were assigned randomly in equal numbers to control or bST injections (500 mg in a prolonged-release form every 14 d for 12 wk) within three stages of lactation (57 to 100, 101 to 140, and 141 to 189 d postpartum) and two parity groups (primiparous and multiparous). Yield and milk composition were monitored 1 d/wk for 16 wk including 2 wk pretreatment and 2 wk posttreatment. Increases in milk and FCM due to bST injections were less at 57 to 100 d than at 101 to 189 d postpartum (milk 3.6 vs. 5.5; FCM 3.9 vs. 6.1 kg/d per cow), and increases in milk and FCM were more for multiparous than for primiparous cows (milk 5.5 vs. 4.2; FCM 6.0 vs. 4.7 kg/d cow). Temporarily, concentration of milk fat increased and protein decreased; later, concentrations for control and injected cows were similar. Postinjection milk fat concentration decreased, but milk protein concentration increased temporarily. The net increase in milk (and FCM) varied significantly among herds from 2.9 to 7.6 kg/d per cow (mean, 4.9 kg). Responses in FCM were similar over a wide range of pretreatment yields. A great variety of feed ingredients were fed as total mixed rations, and nutrient concentrations varied greatly. The SCC were similar before, during, and after treatment, but increase in FCM of injected cows exhibited a negative correlation with pretreatment SCC. Changes in body condition score of sometribove-injected cows varied among herds (.25 to -.45) and averaged -.02 compared with .07 for controls. There was no pattern in incidence of mastitis during sometribove injections.

Animal Feed↗
PubMed1991

Measuring severity of illness: six severity systems and their ability to explain cost variations.

This paper presents results from a study that used a common set of patient records to compared how well different severity measurement systems are able to explain the variations in estimated costs among hospital patients. The systems examined were: APACHE II, MedisGroups, Computerized Severity Index (CSI), Disease Staging, Patient Management Categories (PMCs), and Acuity Index Method. In regressions on costs, all of the measures were found to improve upon DRGs for some types of cases but to offer little or no improvement for others. Indicators of maximum severity, especially Max CSI, explained greater proportions of cost variation than measures of admission severity and measures based on discharge abstracts. In most of the analyses, PMCs and Disease Staging yielded somewhat higher R2 values than the measures of admission severity.

Abstracting and Indexing↗
PubMed1990

VH and VL gene usage by murine IgG antibodies that bind autologous insulin.

To assess the recognition structures of antibodies that bind a self-Ag, we used mRNA analysis to identify the V region genes of IgG antibodies that bind autologous insulin. Four anti-insulin mAb from primary immunization of BALB/c mice use different combinations of H and L chain V region genes. Two VH genes are from the V-gam 3-2 and V-gam 3-8 families that are infrequently expressed in adult BALB/c mice, and two VH genes are members of the J558 family. Each anti-insulin antibody uses a different Vk gene family. Two antibodies express common Vk genes (Ox1 and Vk21C), whereas two other Vk genes are unusual in BALB/c mice. One Vk gene may represent a BALB/c equivalent of the VkOx2 subfamily and another is identical to a Vk used by anti-idiotypic antibodies from C57Bl/6 mice. When compared with known germ-line counterparts, all of the Vk sequences are close to germ-line configuration. In contrast, the germ-line counterparts for the anti-insulin VH genes are not known, however, they differ only in five to seven predicted amino acids from VH of other expressed antibodies. One antibody (mAb 123) differs in one amino acid in complementarity-determining regions 1 and 2 from the VH of the murine tumor BCL1, and another (mAb 126) employs an unmutated DFL16.1 germ-line D segment. These data suggest that antibodies binding autologous insulin use V gene components that are not extensively mutated, even when derived by immunization with heterologous insulin.

Amino Acid Sequence↗
PubMed1990

Guanine nucleotide modulation of [3H]TCP binding to the NMDA receptor complex.

Guanine nucleotides have been examined for their effect on [3H]1-[1-(2-thienyl)-cyclohexyl]-piperidine ([3H]TCP) binding to rat forebrain synaptic plasma membranes (SPM). We report that of the series of guanine nucleotides tested, GTP, GDP, 5'-guanylylimidodiphosphate (Gpp(NH)p) and 5'-guanylylmethylenediphosphate (Gpp(CH2)p) are significantly more potent at decreasing [3H]TCP binding than GMP, cyclic GMP, and guanosine. GTP, the most potent compound tested, inhibited basal [3H]TCP binding with an IC50 of 38.7 microM. Stimulation of [3H]TCP binding with either the N-methyl-D-aspartate (NMDA) agonist, L-glutamate, or Mg2+ was also inhibited by GTP. Addition of GTP resulted in a rightward shift in the glutamate dose-response curve and a decrease in the maximum level of stimulation. The Mg2+ stimulation of [3H]TCP binding was completely blocked by the addition of GTP. These results, coupled with the previous findings that guanine nucleotides inhibit the binding of L-[3H]glutamate to the NMDA recognition site (Monahan et al., 1988), indicate that guanine nucleotides antagonize NMDA receptor-mediated neurotransmission, at least in part, through their action (direct or indirect) on the NMDA recognition site and thus may be endogenous negative modulators of the NMDA receptor.

Animals↗
PubMed1990

Neural control of glutamine synthetase activity in rat skeletal muscles.

The mechanism of glutamine synthetase induction in rat skeletal muscle after denervation or limb immobilization was investigated. Adult male rats were subjected to midthigh section of the sciatic nerve. At 1, 2, and 5 h and 1, 2, and 7 days after denervation, rats were killed and denervated, and contralateral control soleus and plantaris muscles were excised, weighted, homogenized, and assayed for glutamine synthetase. Glutamine synthetase activity increased approximately twofold 1 h after denervation in both muscles. By 7 days postdenervation enzyme activity had increased to three times the control level in plantaris muscle and to four times the control level in soleus muscle. Increased enzyme activity after nerve section was associated with increased maximum velocity with no change in apparent Michaelis constant. Immunotitration with an antiglutamine synthetase antibody suggested that denervation caused an increase in the number of glutamine synthetase molecules in muscle. However, Northern-blot analysis revealed no increase in the steady-state level of glutamine synthetase mRNA after denervation. A mixing experiment failed to yield evidence for the presence of a soluble factor involved in regulating the activity of glutamine synthetase in denervated muscle. A combination of denervation and dexamethasone injections resulted in additive increases in glutamine synthetase. Thus the mechanism underlying increased glutamine synthetase after denervation appears to be posttranscriptional and is distinct from that of the glucocorticoid-mediated glutamine synthetase induction previously described by us.

Animals↗
PubMed1990

Recognition of common islet antigen by autoantibodies from NOD mice and humans with IDDM.

Previous studies showed that islet cell autoantibodies are present at the onset of insulin-dependent diabetes mellitus (IDDM) in humans and in rodent models of this disease. The targets of these antibodies are not well characterized. Using an immunoblot assay on protein extracts from rat insulinoma (RIN) cells (RINm5F), we showed that serums from nonobese diabetic (NOD) mice bind to a 52,000-Mr islet cell antigen. Nondiabetic NON mice do not have antibodies to this antigen. The NOD and NON serums also contained antibodies to salivary gland proteins. Analysis of the tissue distribution of the 52,000-Mr antigen revealed that it is present in purified RINm5F membranes but is not found in other endocrine or nonendocrine tissues. Autoantibodies to an antigen of similar molecular weight are detected in 29% of human IDDM serums. To determine whether the autoantibodies from mouse and human serums bind the same antigen, two-dimensional immunoblots were carried out. The 52,000-Mr protein isoforms appeared identical when probed with NOD and human IDDM serums. We conclude that serums from NOD mice and some humans with IDDM contain similar autoantibodies to a 52,000-Mr RINm5F cell-specific membrane protein. The presence of autoantibodies to this 52,000-Mr islet cell protein at the onset of the disease suggests that it may be an important antigen in IDDM.

Animals↗
PubMed1990

Effects of dietary amines on small intestinal variables in neonatal pigs fed soy protein isolate.

Six litters of newborn crossbred piglets were utilized to examine 1) the effects of substituting 20% of the protein of an all-milk protein liquid diet with a soy protein isolate (milk-soy diet) on small intestinal variables and 2) the effects of supplementing this milk-soy diet with 25 g of either putrescine or ethylamine per kilogram diet on small intestinal variables. Small intestinal xylose absorption tended to increase from wk 1 to wk 2 of age in pigs fed the milk, putrescine and ethylamine diets, but not in pigs fed the milk, putrescine and ethylamine diets, but not in pigs fed the unsupplemented milk-soy diet. Crypt depth in pigs fed the milk-soy diet tended to be less (9.4%; P greater than .10) than the crypt depth in pigs fed the other diets, but mitotic index was not different (P greater than .10) among diets. Mucosal protein, DNA and RNA concentrations and mucosal brush border sucrase and cytosolic dipeptidase activities tended to be least in pigs fed the putrescine and ethylamine diets. Concentration of mucosal putrescine was greatest (P less than .002) in the distal regions of the small intestine of pigs fed putrescine. Mucosal ornithine decarboxylase activity was inhibited by putrescine (P less than .02), but it was not affected by the soybean protein isolate used in this study. Supplementing soy protein isolate diets with amines may enhance intestinal absorption and enterocyte proliferation.

Amines↗
PubMed1990

Autoantibodies present at onset of type I diabetes recognize multiple islet cell antigens.

Antibodies to islet antigens are useful markers of the pathological process that results in destruction of beta cells in type I diabetes. The targets of these antibodies, however, are not well characterized and their role in the pathological process remains to be established. To better understand the range of antigens recognized by autoantibodies in type I diabetes mellitus, we carried out immunoblotting on protein extracts from human islet and rat insulinomas. Using this approach higher titer antibodies specific for islet antigens were detected in 20/28 sera from recent onset type I diabetics and were infrequent (4/28) in sera from age-matched controls. Sera from diabetics reacted with multiple antigens at titers from 1/100-1/4000 while control sera usually bound a single band at lower dilutions. Although antigens of Mr 52, 84, 116 and 150 kilodalton were recognized most frequently, no antigen was bound by more than 50% of diabetic sera. Some of these antigens enriched in the membrane fraction while others were not. The data demonstrate that a heterogenous group of islet antigens is recognized by autoantibodies present at the onset of type I diabetes when islet destruction is complete. These findings contrast previous reports using immunoprecipitation with undiluted sera that principally identify a 64 kDa islet antigen. Thus, the immunoblot technique detects a different set of reactivities than previously identified by immunoprecipitation. The pattern of multiple reactivities with both surface and cytoplasmic antigens suggest that many autoantibodies may be generated by beta cell destruction and some of these may amplify the ongoing immune response.

Animals↗
PubMed1989

Insulin B chain functions as an effective competitor of antigen presentation via peptide homologies present in the thymus.

The B chain of mammalian insulins contains appropriately spaced amino acids that predict recognition by T cells. However, all T cell clones from an HLA-DR1, Dw6 diabetic donor recognize epitopes associated with the A chain, and the B chain was found to inhibit these responses. Effective intramolecular competition at the level of the APC, not a direct effect on the T cell, is responsible for the inhibition. Insulin B chain contains two clusters of amino acid homology with the TCR beta chain and B chain peptides lacking these clusters do not compete for antigen presentation. A hole in the repertoire for T cells that recognize this portion of the insulin molecule may arise in the thymus by deletion of T cells that recognize similar peptides.

Amino Acid Sequence↗