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R M Little

Publications and source records attributed to R M Little.

At least 37 records · Page 2Linked to original sources
PubMed1987

Preliminary X-ray crystallographic study of cyanase from Escherichia coli.

Cyanase, an oligomeric enzyme of Escherichia coli that catalyzes the decomposition of cyanate to ammonia and bicarbonate, crystallizes in the space group P1 with unit cell parameters a = 85.96 A, b = 83.17 A, c = 83.28 A, alpha = 110.29 degrees, beta = 118.29 degrees and gamma = 72.40 degrees. Crystals diffract to a resolution of at least 2.5 A. The crystal data, in conjunction with a subunit molecular weight of 17,008, suggest that two oligomers are in the asymmetric unit of the crystal and that eight subunits comprise a single oligomer.

Aminohydrolases↗
PubMed1987

Structural properties of cyanase. Denaturation, renaturation, and role of sulfhydryls and oligomeric structure in catalytic activity.

Cyanase is an inducible enzyme in Escherichia coli that catalyzes bicarbonate-dependent decomposition of cyanate to give ammonia and bicarbonate. The enzyme is composed of 8-10 identical subunits (Mr = 17,008). The objective of this study was to clarify some of the structural properties of cyanase for the purpose of understanding the relationship between oligomeric structure and catalytic activity. Circular dichroism studies showed that cyanase has a significant amount of alpha-helix and beta-sheet structure. The one sulfhydryl group per subunit does not react with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) unless cyanase is denatured. Denaturation is apparently complete in 10 M urea or 6 M guanidine hydrochloride, but is significantly reduced in 10 M urea by the presence of azide (analog of cyanate) and is incomplete in 8 M urea. Denatured cyanase could be renatured and reactivated (greater than 85%) by removal of denaturants. Reactivation was greatly facilitated by the presence of certain anions, particularly bicarbonate, and by high ionic strength and protein concentration. The catalytic activity of renatured cyanase was associated only with oligomer. Cyanase that had been denatured in the presence of DTNB to give a cyanase-DTNB derivative could also be renatured at 26 degrees C to give active cyanase-DTNB oligomer. The active oligomeric form of the cyanase-DTNB derivative could be converted reversibly to inactive dimer by lowering the temperature to 4 degrees C or by reduction of the ionic strength and removal of monoanions. These results provide evidence that free sulfhydryl groups are not required for catalytic activity and that catalytic activity may be dependent upon oligomeric structure.

Aminohydrolases↗
PubMed1987

Interaction of mono- and dianions with cyanase: evidence for apparent half-site binding.

Cyanase is an inducible enzyme in Escherichia coli that catalyzes bicarbonate-dependent hydrolysis of cyanate. The dianions oxalate, oxalacetate, and malonate are slow-binding inhibitors of cyanase, and some monoanions such as azide and chloride also inhibit cyanase activity [Anderson, P. M., & Little, R. M. (1986) Biochemistry 25, 1621-1626]. The purpose of this study was to investigate the interaction of selected dianions and monoanions by kinetic and equilibrium dialysis binding studies in an effort to obtain information about the active site and catalytic mechanism. Measurement of the effectiveness of 30 different dianions as inhibitors of cyanase showed a significant degree of structural and/or isomeric specificity and considerable variation with respect to the slow-binding nature of the inhibition. Oxalate and oxalacetate both show extreme slow-binding inhibition at very low concentrations. Kinetic studies of the rate of inhibition of cyanase by oxalate showed that the reaction is pseudo first order with respect to oxalate concentration and the results are consistent with a pathway in which oxalate forms a complex with the enzyme in a rapid initial reversible step followed by a slow isomerization step leading to a complex with a very low dissociation constant. The rate of inhibition is significantly reduced by the presence of relatively low concentrations of either azide (analogue of cyanate) or bicarbonate. Equilibrium dialysis binding studies showed that the stoichiometry of binding at saturation for oxalate, malonate, chloride, and bicarbonate is about 0.5 mol of ligand bound/mol of subunit for each compound.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminohydrolases↗
PubMed1986

Kinetic properties of cyanase.

Cyanase is an inducible enzyme in Escherichia coli that catalyzes the hydrolysis of cyanate. Bicarbonate is required for activity, perhaps as a substrate, and the initial product of the reaction is carbamate, which spontaneously breaks down to ammonia and bicarbonate [Anderson, P. M. (1980) Biochemistry 19, 2882]. The purpose of this study was to characterize the kinetic properties of cyanase. Initial velocity studies showed that both cyanate and bicarbonate act as competitive substrate inhibitors. A number of monovalent anions act as inhibitors. Azide and acetate appear to act as competitive inhibitors with respect to cyanate and bicarbonate, respectively. Chloride, bromide, nitrate, nitrite, and formate also inhibit, apparently as the result of binding at either substrate site. Malonate and several other dicarboxylic dianions at very low concentrations display "slow-binding", reversible inhibition which can be prevented by saturating concentrations of either substrate. The results are consistent with a rapid equilibrium random mechanism in which bicarbonate acts as a substrate, bicarbonate and cyanate bind at adjacent anion-binding sites, and both substrates can bind at the other substrate anion binding site to give a dead-end complex.

Aminohydrolases↗
PubMed1985

Anterior open-bite malocclusion: a longitudinal 10-year postretention evaluation of orthodontically treated patients.

Long-term response of the anterior open-bite malocclusion was evaluated in forty-one white subjects who had undergone orthodontic treatment and were out of retention a minimum of 9 years 6 months. The purpose of the study was threefold: (1) to make cephalometric comparisons between a sample of open-bite patients and a sample with normal cephalometric standards, (2) to evaluate treatment and posttreatment changes that occurred in treated open-bite patients, and (3) to search for predictors and associations of value. Changes occurring across time in the open-bite patients were analyzed by computer means using pretreatment, posttreatment, and long-term cephalometric radiographs and dental casts. An analysis of subgroups was reviewed to compare dentoalveolar and skeletal relationships of both stable and relapse groups. More than 35% of the treated open-bite patients demonstrated a postretention open bite of 3 mm or more, with the relapse subgroup demonstrating across-time, less mandibular anterior dental height, less upper anterior facial height, greater lower anterior facial height, and less posterior facial height. Neither the magnitude of pretreatment open bite, mandibular plane angle, nor any other single parameter of dentofacial form proved to be a reliable predictor of posttreatment stability.

Adolescent↗
PubMed1985

Stability and relapse of mandibular anterior alignment: a cephalometric appraisal of first-premolar-extraction cases treated by traditional edgewise orthodontics.

Assessment at least 10 years postretention of fifty-four cases previously treated in the permanent-dentition stage with first-premolar extractions, traditional edgewise mechanotherapy, and retention revealed considerable variation among patients. The long-term response to mandibular anterior alignment was unpredictable; no cephalometric parameters, such as maxillary and mandibular incisor proclination, horizontal and vertical growth amounts, mandibular plane angle, etc., were useful in establishing a prognosis. Few associations of value were found between cephalometric parameters and dental-cast measurements, such as overbite, arch length, intercanine width, and overjet. Only a slight tendency was found for incisor inclination to return toward the pretreatment value during the postretention period. It was possible to predict, on the basis of an analysis of pre- and posttreatment cephalometric records, those cases which had greater than 4 mm deepening of overbite postretention as well as those cases which had decreases of 3 mm or more in arch-length postretention. The practical use of these predictions were of limited clinical value, however.

Adolescent↗
PubMed1985

Dentofacial maturation of untreated normals.

Cephalometric head films from a sample of 65 untreated normal persons were evaluated to determine the nature and extent of the normal dentofacial maturation process. Thirty-four parameters were examined in the mixed dentition (9 to 10 years), the early permanent dentition (12 to 13 years), and early adulthood (19 to 20 years). Results showed the importance of maxillary development, particularly in the vertical plane, as it was associated with the amount and direction of sagittal mandibular growth. "Late mandibular growth" was found to be a forward (bite-closing) rotation of the mandible that occurred after the cessation of vertical maxillary growth. Condylar growth amount and direction were influential in determining the degree of sagittal mandibular change. The degree of forward (bite-closing) mandibular rotation was strongly associated with the amount of both maxillary and mandibular molar eruption. Incisor positions were found to remain relatively constant, showing compensations for the amount and direction of skeletal growth. No correlations or predictions of clinical value were found between the cephalometric parameters examined and previously recorded dental-cast variables.

Adolescent↗
PubMed1984

Mandibular incisor dimensions and crowding.

Previous authors have suggested that well-aligned mandibular incisors are narrower mesiodistally than incisors which crowd and that reducing mesiodistal dimensions of the mandibular incisors to fit a specific size range will prevent future malalignment. This study examined 164 cases from the records of the University of Washington Department of Orthodontics, 134 of which had been orthodontically treated and were a minimum of 10 years postretention. Measurements were made from the postretention plaster casts and from serial cephalometric head films. Statistical tests showed that there was a weak association between incisor widths or MD/FL dimensions ratio and irregular alignment over the long term. Mean dimensional differences between crowded and uncrowded incisors were small in the few pooled or segregated groups in which statistically significant differences were found. When incisor dimensions were combined with pretreatment, posttreatment, or long-term cephalometric and cast measurements, only weak and not clinically useful associations were found with long-term incisor alignment. While there was a weak tendency for narrower incisors to be associated with better alignment in some instances, narrower mesiodistal widths of mandibular incisors did not ensure long-term stability in orthodontically treated cases.

Adult↗
PubMed1983

The effect of extraction and orthodontic treatment on dentoalveolar support.

Full-mouth radiographs of ninety-six patients treated by extraction of four first premolars were taken at least 10 years postextraction. Three groups were established: one with extensive crowding in the full permanent dentition treated by extraction and fixed appliance therapy; one treated by serial extraction and fixed appliance therapy; and one treated by serial extraction only. Measurements of tooth length and alveolar bone height were made from the projected radiographs, and buccolingual socket areas were measured from direct tracings of the radiographs. Comparison between groups revealed reduced mean radiographic tooth lengths for incisors and mandibular molars in the orthodontically treated groups. The incidence of root resorption was similar for both treated groups. Reduced alveolar bone heights were noted in the extraction sites of the two orthodontically treated groups but not in the group treated by serial extraction only. Most reduction in long-term dentoalveolar support occurred as a result of root resorption except in the extraction sites, where it occurred largely as a result of bone loss. Root parallelism did not appear to influence proximal bone heights at the extraction site. In malocclusions involving arch length deficiency, maximally displaced canines had reduced long-term proximal bone compared to nondisplaced canines, supporting the concept of encouraging autonomous distal eruption through serial extraction.

Adult↗
PubMed1983

Maturation of untreated normal occlusions.

The dental casts of 65 untreated normal occlusions were evaluated to determine the nature and extent of the developmental maturation process of the normal dentition. Six dental parameters were examined in the mixed dentition (9 to 10 years), early permanent dentition (12 to 13 years), and early adulthood (19 to 20 years). Results showed decreases in arch length and intercanine width; minimal overall changes in intermolar width, overjet, and overbite; and increases in incisor irregularity. Females showed more severe changes than males. The individual changes found were not correlated to changes in any of the other parameters measured. No associations or predictors of clinical value were found. The changes found in a sample of untreated normals were similar in nature but lesser in extent than postretention changes found in a sample of treated cases.

Adolescent↗
PubMed1981

Stability and relapse of mandibular anterior alignment-first premolar extraction cases treated by traditional edgewise orthodontics.

Assessment at least 10 years postretention of sixty-five cases previously treated in the permanent-dentition stage with first-premolar extractions, traditional edgewise mechanics, and retention revealed considerable variation among patients. The long-term response to mandibular anterior alignment was unpredictable; no variables, such as degree of initial crowding, age, sex, Angle classification, etc., were useful in establishing a prognosis. Typically, arch width and length decreased after retention, regardless of treatment expansion or constriction. Two thirds of the patients had unsatisfactory lower anterior alignment after retention. Cases that were minimally crowded before treatment usually became more crowded, while initially severe crowding cases usually moderated.

Adolescent↗
PubMed1981

Surgical mandibular advancement: a cephalometric analysis of treatment response.

Fifty-two cases of surgical advancement of the mandible were evaluated by retrospective cephalometric and computer analysis for longitudinal skeletal and dental changes an average of 3 1/2 years after surgery. Postsurgical treatment response appeared to be a multifactorial biologic phenomenon with considerable individual variability. Results showed generally good stability after mandibular advancement, with a minimal to moderate tendency toward skeletal relapse during intermaxillary fixation. Positional change of the proximal segment was the most important parameter in determining stability or relapse of the advanced mandible. Anteroinferior displacement of the condyle and increased posterior facial height were found to be important factors in the skeletal relapse observed during the period of intermaxillary fixation. The magnitude of mandibular advancement was a reliable surgical predictor of postsurgical relapse. Preoperative mandibular plane angle, postfixation intersegment instability, and patient's age cannot be isolated as being solely responsible for specific postsurgical changes.

Adolescent↗
PubMed1980

An interdisciplinary teacher education program.

In 1975 the faculty of the University of Washington School of Dentistry, in conjunction with the College of Education and the affiliated Children's Orthopedic Hospital and Medical Center, developed a 36-month formal teacher education program in combination with joint specialty training in pedodontics and orthodontics. The program goal was to produce a professional dental educator/administrator who could function primarily in the teaching and practice of child and adolescent comprehensive care. After four years and three graduates, the faculty terminated this program. This paper outlines the rationale and structure of the original program and discusses the reasons for its termination.

Curriculum↗
PubMed1975

The irregularity index: a quantitative score of mandibular anterior alignment.

A quantitative method of assessing mandibular anterior irregularity is proposed. The technique involves measurement directly from the mandibular cast with a caliper (calibrated to at least tenths of a millimeter) held parallel to the occlusal plane. The linear displacement of the adjacent anatomic contact points of the mandibular incisors is determined, the sum of the five measurements representing the Irregularity Index value of the case. Reliability and validity of the method were tested, with favorable results. At the University of Washington, several clinical studies have been and are continuing to be performed, using this technique as one of several methods of assessing pretreatment status and posttreatment change. It is hoped that this article will aid the reader in understanding the rationale and utility of a simple quantitative tool which could be used in malocclusion assessment.

Analysis of Variance↗