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Biomedical subjects

L J Harris

Publications and source records attributed to L J Harris.

At least 37 records · Page 2Linked to original sources
PubMed1999

Nisin reduces the thermal resistance of Listeria monocytogenes Scott A in liquid whole egg.

D-values (decimal reduction times) and z-values (increase in temperature required for a 1-log change in D-value) for Listeria monocytogenes Scott A were determined in liquid whole egg with nisin (0 or 10 microg ml(-1)) and NaCl (0 or 10%) by a submerged glass ampoule procedure. Samples were plated onto nonselective agar at appropriate intervals, and D-values were determined using a modified biphasic logistic equation. Addition of NaCl increased D-values at all temperatures tested. The addition of nisin to unsalted liquid whole egg resulted in a rapid 4-log reduction in viable counts within the first hour. Nisin significantly (P < or = 0.05) decreased D-values at lower (< 58 degrees C) temperatures in both unsalted and salted liquid whole egg but had little effect on the D-values at current minimum U.S. and Canadian pasteurization temperatures (60 degrees C without NaCl; 63 degrees C with NaCl). However, when nisin was added 2 h prior to heat treatment, D-values were significantly (P < or = 0.05) reduced at these temperatures. Inhibitory levels of nisin were detected in the liquid whole egg postpasteurization. Nisin could have a favorable impact on the control of L. monocytogenes in pasteurized liquid egg products.

Animals↗
PubMed1998

Crystallographic structure of an intact IgG1 monoclonal antibody.

The structure of an intact monoclonal antibody for phenobarbital, subclass IgG1, has been determined to 3.2 A resolution by X-ray crystallography. The molecule was visualized in a monoclinic unit cell having an entire immunoglobulin as the asymmetric unit. The two Fab segments, both with elbow angles of 155 degrees , were related by a rotation of 179.7 degrees plus a translation along the approximate dyad of 9 A. This is the first observation of such an Fab translation in a structurally defined antibody. The approximate 2-fold of the Fc was independent of that relating Fabs, making an angle of 107 degrees with the Fab dyad. The angle between long axes of the Fabs was 115 degrees, the most acute angle yet observed, yielding a distorted Y shaped molecule. This is in contrast to the distorted T shape of the only other intact IgG (2a) whose complete structure is known. Primary lattice interactions arise through formation of VH antiparallel beta ribbons whose strands are contributed by pseudo dyad related H2, and by L3 hypervariable loops from neighboring molecules. While one CH2 domain was mobile, Fabs and three domains of the Fc were well defined, as were hinge polypeptides connecting Fabs to the Fc, and the covalently attached oligosaccharides. Direct interactions are observed between hinge polypeptides, the glycosylated loop of one CH2 domain, and the oligosaccharide. Lattice interactions clearly influence, perhaps even determine the overall conformation of the antibody observed in this crystal. Comparison of this IgG1 with previously determined intact antibody structures extends the conformational range arising from segmental flexibility.

Amino Acid Sequence↗
PubMed1998

Comparison of the conformations of two intact monoclonal antibodies with hinges.

Structures of two intact monoclonal antibodies were solved by X-ray diffraction analysis revealing, in both cases, the dispositions of all segments, as well as the structures of the hinge polypeptides. An IgG1, whose antigen is the drug phenobarbital, assumed a completely different conformation when compared with an IgG2a specific for canine lymphoma cells. Though neither IgG displays global two-fold symmetry, both maintain two pseudo dyad axes, one relating Fab segments, and the other the halves of the Fc. In both IgGs, the Fc segment is obliquely disposed with respect to the plane of the Fabs, making an angle of 128 degrees in the IgG2a, and 107 degrees in the IgG1. Hinge angles of the IgG1 are notably different at 78 degrees and 123 degrees, and unique as well from IgG2a values of 66 degrees and 113 degrees. Elbow angles within the IgG1 Fabs are the same at 155 degrees, but non-identical in IgG2a where they took on values of 143 degrees and 159 degrees. The IgG2a has an angle of 172 degrees between Fabs so that it exhibits a "distorted T" shape, whereas that angle in the IgG1 is a much more acute 115 degrees producing a "distorted Y". CH2 domains appear, in both antibodies, to be the most independently mobile of the paired IgG domains. This perhaps reflects their importance in modulating effector functions through exposure of binding loci on the CH2, at the CH2-CH3 interface, and on lower hinge polypeptides. Hinges in both antibodies contain disulfide-linked cores bounded by fluid regions above and below, which provide mobility to the Fabs and Fc respectively. The conformations seen in these two structures are undoubtedly only two among many but they illustrate the modes of flexibility inherent to the IgG architecture.

Animals↗
PubMed1998

Human classical conditioning of visual compound stimuli in paired-associate tasks.

College students in introductory psychology participated in four experiments to investigate the salience of color versus figure elements of paired associates. The study also reviewed the process of learning paired associates within the context of first-order simultaneous classical conditioning. In Exp. 1, four separate classes received different treatments concerning the position and type of stimulus element (color of figure) they were instructed to recall. There were seven trials with a 30-min. delay between the sixth and seventh trials. The results indicated that the groups who were required to remember the figure element of the pairs, significantly out-performed the color groups and also learned the pairs much faster. Also, there was a sharp rise in mean correct responses remembered after a 30-min. delay for the group required to recall the color element of the paired associates. Exp. 2 was a within-subjects comparison of the effectiveness of the color and figure elements as stimuli. Again, the figures elicited more correct responses than colors. Exp. 3 tested the effectiveness within subjects of the stimulus elements as response factors. As responses, however, there were no significant differences in the number of correct answers when recalling color or figure elements until the 30-min. delay between Trials 6 and 7. As expected in Exp. 4, figures elicited significantly more functional descriptions than did colors, suggesting that figures possess a logographic nature which acts as a mnemonic device aiding in the memory of stimuli and responses.

Color Perception↗
PubMed1997

Refined structure of an intact IgG2a monoclonal antibody.

The structure of an intact, anti-canine lymphoma monoclonal antibody (Mab231) was determined by molecular replacement and refined in a triclinic cell to an R-value of 20.9%, using synchrotron diffraction data from 2.8 to 20 A resolution. All segments of the antibody, including the hinge region and carbohydrate component, are visible in electron density maps. There is no overall symmetry to the antibody, as the Fc is disposed in an entirely oblique manner with respect to the Fabs. The CH2 and CH3 domains do, however, possess a nearly exact, local 2-fold relationship. The Fab segments are related by a second, independent, local dyad axis, exact only with respect to constant domains. Variable domains exhibit no symmetry relationship as a consequence of the 16 degrees difference in Fab elbow angles. Variable domain pair associations VL:VH for the Fabs are virtually the same, and corresponding CDRs of the two Fabs also are nearly identical in structure. CDR-H3 displays the greatest difference. Hypervariable loops of both Fabs are involved in contacts with symmetry-related Fc segments at the CH2-CH3 switch junction, suggesting a "complex" structure. The hinge segment connecting Fabs with the Fc is quite extended and exhibits thermal factors indicative of a high degree of mobility. It consists of a well-defined upper hinge that partially maintains dyad symmetry and a fairly rigid core bounded above and below by fluid polypeptides that provide segmental flexibility. This structure represents the first visualization by X-ray analysis of a murine Fc segment, and its CH2 domains exhibit substantial rigid body conformational changes with respect to the human Fc used as an initial molecular replacement model. The oligosaccharides were found by difference Fourier syntheses to be very similar to those of the free human Fc fragment, although differences are present in the terminal residues. The detailed structure of the IgG presented here, and the distribution of effector binding sites, appears consistent with effector activation mechanisms involving translocation and/or aggregation of the Fc following antigen binding by the Fabs.

Amino Acid Sequence↗
PubMed1997

Cerebral anesthesia for localization of speech: the contribution of W. James Gardner.

In 1949, the neurologist Juhn Wada reported the first use of a new procedure for determining the localization of speech and language in neurological patients: examination of the effects on speech and language after injecting a barbiturate, sodium amytal, into the internal carotid artery of each hemisphere in succession. By the 1960's, Wada's Intracarotid Amobarbital Procedure, or IAP, had become the method of choice for identifying the speech-dominant side in one kind of neurological patient, persons with epilepsy who are candidates for surgical resection, and it remains so today. In 1941, however, an American neurosurgeon, W. James Gardner, reported his use of a different anesthetization procedure for speech localization in neurological patients. Instead of injecting sodium amytal through the blood supply, as in IAP, Gardner injected procaine hydrochloride directly into cortical tissue. In this paper, we provide a brief biography of Gardner. We then discuss his method of cortical anesthetization, the theoretical and empirical background guiding his use of this method and his choice of patients, and, finally, the fate of Gardner's method within the scientific community.

Amobarbital↗
PubMed1997

The intracarotid amobarbital procedure: an historical perspective.

The intracarotid sodium amobarbital procedure (IAP) is currently regarded as the best method of the determination of hemispheric specialization for speech, and it is universally relied on as a prognostic test for patients with medically refractory epilepsy who are candidates for neurosurgical intervention. Since its initial development, the IAP also has been adapted for assessing lateralized mesiotemporal contributions to memory functioning in this patient population, and it is now in wide use for both basic and applied research in behavioral neuroscience on language, memory, visuospatial functions, emotion, attention, and consciousness. Despite the IAP's wide range of applications, little has been said about its history and development. This essay recounts and discusses this history.

Amobarbital↗
PubMed1997

Lexicon size and its relation to foot preference in the African grey parrot (Psittacus erithacus).

To study footedness in parrots, an international survey of parrot owners was conducted. Responses were obtained from 524 individuals, including 70 owners of African Grey parrots (all animals > or = 10 months old). All respondents were given a 10-item questionnaire and a standard method for testing foot preference in their pets, and they were asked to count the number of separate words in their pets' lexicons of human speech sounds. Right-footed African Greys (N = 36) had significantly larger lexicons than left-footed African Greys (N = 34; P = 0.01). This difference could not be accounted for by group differences in training efforts or socialization/housing with conspecifics. A non-significant trend in the same direction was found in a comparison sample of Amazon parrots, although these genera are less adept than African Greys at learning human speech sounds. Other investigators have provided convincing evidence of lateralization, in the avian brain, for the analysis and memory of differing types of stimuli. In addition, there appears to be preferential left hypserstriatal activation for long-term memory consolidation. Our results suggest a relationship between lateral asymmetry for motor preference and asymmetric CNS mediation of a 'higher cognitive' function (i.e. the categorization and long-term mnestic processing of human speech sound.

Animals↗
PubMed1996

A combinatorial library strategy for the rapid humanization of anticarcinoma BR96 Fab.

We have used a combinatorial mutagenesis strategy to humanize BR96, a monoclonal antibody that binds to the Lewis Y class of tumor antigens. This approach allows simultaneous assessment of hundreds of humanized variable regions to identify the molecules that best preserve affinity, thus overcoming the major drawback of current humanization procedures, the requirement to construct and analyze each humanized antibody separately. Murine residues of BR96 were mutated to human if they were solvent-exposed residues that did not participate in the formation of the antigen binding site and were not at the interface of the light and heavy chain. At positions that might be involved in binding to antigen, the choice between the murine and human residue was more difficult. Murine and human alternatives were incorporated into a combinatorial library at positions representing buried residues that might affect the structural integrity of the antigen binding site. By encoding this library of humanized BR96 Fabs in an M13 phage vector, we rapidly identified several candidates with nearly identical antigen binding, within 2-fold, of the chimeric Fab. Additional mutagenesis directed at sites suggested in the literature as potentially important for antigen binding in a similar anti-Lewis Y antibody yielded no further improvements.

Amino Acid Sequence↗
PubMed1996

Accuracy of college students' reports of parental handedness.

College students' reports of their parents' handedness were compared with data provided by the parents themselves. The students' reports of their parents' writing hand were highly accurate, the reports of their parents' general handedness somewhat less so. For the latter measure, the students were asked, ''What is your mother's (father's) handedness?'' and were given the choice ''left'',''either'', ''right'',and ''don't know''. Their answers were then compared with the investigators' classification based on the parents' answers to a 10-item hand-use questionnaire. For this measure, the accuracy of the students' reports was also found to be related to the students' own handedness.

Journal Article↗
PubMed1996

Where in the world am I? Sex and handedness differences in knowledge of geography.

218 college students (96 men and 122 women, including nearly equal numbers of right-handers and left-handers) were administered a modified version of the "Gallup Geography Test." Men outperformed women, and left-handed women outperformed right-handed women. We suggest that these results cannot be easily explained by any credible sociocultural model but are consistent with a neuropsychological model of sex and handedness differences in spatial ability advanced by Harshman, Hampson, and Berenbaum in 1983.

Adolescent↗
PubMed1995

The sole lysine residue in porcine pepsin works as a key residue for catalysis and conformational flexibility.

Pepsin contains a single lysine residue which protrudes from the enzyme's surface, behind the active site cleft, on the C-terminal domain. Mutations of pepsin by site-directed mutagenesis of the Lys-319 residue were generated to study the structure-function relationships. Kinetic parameters, pH activity profiles, along with conformational analysis using circular dichroism (CD), and molecular modelling were examined for the wild-type (non-mutant) and mutant enzymes. The pepsin mutations, Lys-319-->Met and Lys-319-->Glu, resulted in a progressive increase in the Km and similar decrease in kcat, respectively, as well as being denatured at a lower pH than the wild-type pepsin. CD analysis indicated that mutations at Lys-319 resulted in changes in secondary structure fractions which were reflected in changes in enzymatic activity as compared to the wild-type pepsin, i.e. kinetic data and pH denaturation study. Molecular modelling of mutant enzymes indicated differences in flexibility in the flap loop region of the active site, the region around the entrance of the active site cleft, sub-site regions for peptide binding, and in the subdomains of the C-terminal domain when compared to the wild-type enzyme. The results suggest that Lys-319, which is distal to the active site, is important to the flexibility/stability of the enzyme, as well as to its catalytic machinery.

Amino Acid Sequence↗
PubMed1995

Crystallization of intact monoclonal antibodies.

Attempts were made to crystallize four monoclonal antibodies, one IgG2a kappa and three IgG1 kappa. Using a PEG 3350 screen combined with detergents, and developed from our experiments with an IgG2a kappa antibody specific for canine lymphoma cells, crystals have now been obtained of two of these four immunoglobulins, an antiphenytoin and an antiphenobarbital antibody. A complex between the antiphenobarbital antibody and its drug antigen crystallized as well. The antibody for phenytoin has, to this point, produced only clustered microcrystals, marginally suitable for X-ray analysis. Single crystals of the IgG1 kappa antibody against phenobarbital, however, were characterized by X-ray diffraction to be primitive monoclinic, with unit cell dimensions a = 67 A, b = 193 A, c = 74 A, and beta = 110 degrees. These crystals have an entire IgG1 kappa molecule as the asymmetric unit and they diffract to at least 3.2 A resolution.

Animals↗
PubMed1994

Effects of typeface characteristics on visual field asymmetries for letter identification in children and adults.

The current study compared the effects of three typeface characteristics (script-likeness, or resemblance to cursive writing; confusability, or likelihood of confusing one letter with another; and difficulty, as indexed by naming latency) on letter identification in a divided visual fields test. It also asked whether and how these effects change with subject age. Subjects were 48 right-handed 9- and 14-year-old boys and undergraduate men--16 in each age group. They orally identified single letters in eight different typefaces presented tachistoscopically to the left or right visual hemifield. The difference between hemifields in threshold presentation time was the dependent measure. For all ages, the direction and degree of the visual field advantage changed with typeface complexity (a composite index of the three characteristics), with the simplest typeface yielding a right visual field/left hemisphere advantage, and with two of the most complex typefaces yielding a left visual field/right hemisphere advantage. There were age differences, though, in the relative contribution of the individual characteristics to this effect. For undergraduates, the strongest predictor of right hemisphere participation was script-likeness, whereas for 9- and 14-year-olds it was typeface difficulty.

Adolescent↗
PubMed1994

Large tandem duplication associated with a Mu2 insertion in Zea mays B-Peru gene.

The b locus of Zea mays encodes a transcriptional activator of the anthocyanin biosynthetic pathway. The B-Peru allele is expressed in the aleurone layer of the seed, which results in dark purple pigmentation of this tissue. An unstable Mutator-induced B-Peru mutant allele, b-Perum220, displays weak, variable pigment and a high germinal reversion rate not characteristic of other Mutator insertions. Characterization of relevant regions of b-Perum220 revealed a Mu2 element insertion in one copy of a 534 bp sequence. This 534 bp sequence is tandemly triplicated in the progenitor B-Peru allele, upstream of the B-Peru transcription start site. In addition to the Mu2 insertion, the b-Perum220 allele contains a newly formed large tandem duplication of 4.0 kb, which includes the promoter region and the first three exons of the B-Peru gene. The Mu2 element does not reside at any of the duplication breakpoints. The molecular study of eleven independent germinal revertants revealed five structural classes including structures in which the 4.0 kb tandem duplication is partially or completely deleted, the Mu2 element is partially or completely deleted, or a combination of these events has occurred. We hypothesize that most of the revertants arose by unequal recombination between the duplicated regions. Based on these structural analyses, models are discussed to explain the reduced b gene expression in b-Perum220.

Alleles↗
PubMed1994

Characterization of biosynthetic IgG oligomers resulting from light chain variable domain duplication.

We have characterized a human IgG1 monoclonal antibody composed of altered light chains. Each light chain consists of two identical variable domains and a kappa constant domain, in association with a normal gamma chain. This antibody assembled biosynthetically into a mixture of stable oligomers and monomers. Employing gel filtration, PAGE, and electron microscopy, we examined the antibody and the nature of the associations involved in oligomer formation. By engineering a protease factor Xa site between the duplicated light chain variable domains and examining the fragments produced following factor Xa cleavage, we demonstrated the association of the IgG monomers occurred through their duplicated VL domains. Electron microscopy showed the oligomeric antibody to be predominantly dimers and trimers in which the monomeric units were associated through the tips of the Fab portion of the antibody, presumably through the protruding N-terminal VL domains. Similar examination of monomers demonstrated several molecular forms, including individual molecules with self-crosslinked Fab arms and others displaying the open Y and T shapes typically observed for IgG antibodies. The monomers also displayed distally protruding domain-like structures. The oligomers produced by this cell line therefore occurred through the noncovalent interaction between the extra light chain variable domains.

Amino Acid Sequence↗