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Biomedical subjects

M Beck

Publications and source records attributed to M Beck.

At least 217 records · Page 12Linked to original sources
PubMed1994

Mechanical strength of repairs of the rotator cuff.

We have studied the mechanical properties of several current techniques of tendon-to-bone suture employed in rotator-cuff repair. Non-absorbable braided polyester and absorbable polyglactin and polyglycolic acid sutures best combined ultimate tensile strength and stiffness. Polyglyconate and polydioxanone sutures failed only at high loads, but elongated considerably under moderate loads. We then compared the mechanical properties of nine different techniques of tendon grasping, using 159 normal infraspinatus tendons from sheep. The most commonly used simple stitch was mechanically poor: repairs with two or four such stitches failed at 184 N and 208 N respectively. A new modification of the Mason-Allen suture technique improved the ultimate tensile strength to 359 N for two stitches. Finally, we studied the mechanical properties of several methods of anchorage to bone using typically osteoporotic specimens. Single and even double transosseous sutures and suture anchor fixation both failed at low tensile loads (about 140 N). The use of a 2 mm thick, plate-like augmentation device improved the failure strength to 329 N. The mechanical properties of many current repair techniques are poor and can be greatly improved by using good materials, an improved tendon-grasping suture, and augmentation at the bone attachment.

Animals↗
PubMed1994

The hired gun expert witness.

This article briefly discusses the role of the expert physician witness at trial and describes what is emerging as the physician professional witness (AKA hired gun). The trial court's powers to evaluate the professionalism and objectivity of an expert witness are examined in light of a recent Western District Missouri Court of Appeals case. This case, while limited to its peculiar set of facts, permitted both a hearing and production of documents of a physician who had been hired to testify. This article reviews the role of the expert physician witness in Missouri litigation in light of recent caselaw outlining discovery procedures to monitor use of professional witnesses. The term "professional witness" does not refer to witnesses who are professionals, but rather to persons who make their entire living witnessing. The Missouri Court of Appeals ruling in State ex rel. Lichtor v. Clark, 845 S.W.2d (Mo.App. W.D. 1992) elucidates the Missouri Courts' authority in sorting out unprofessional physicians who would offer unobjective expert testimony. While this particular article is intended for medical readership and discusses expert physician witnesses, expert witnesses can come from any profession including engineering, accounting, nursing, etc. It might thus be assumed that the Lichtor Court's procedure may be applied to any expert whose objectivity has been put into question.

Expert Testimony↗
PubMed1993

Protonation states of membrane-embedded carboxylic acid groups in rhodopsin and metarhodopsin II: a Fourier-transform infrared spectroscopy study of site-directed mutants.

A method was developed to measure Fourier-transform infrared (FTIR) difference spectra of detergent-solubilized rhodopsin expressed in COS cells. Experiments were performed on native bovine rhodopsin, rhodopsin expressed in COS cells, and three expressed rhodopsin mutants with amino acid replacements of membrane-embedded carboxylic acid groups: Asp-83-->Asn (D83N), Glu-122-->Gln (E122Q), and the double mutant D83N/E122Q. Each of the mutant opsins bound 11-cis-retinal to yield a visible light-absorbing pigment. Upon illumination, each of the mutant pigments formed a metarhodopsin II-like species with maximal absorption at 380 nm that was able to activate guanine nucleotide exchange by transducin. Rhodopsin versus metarhodopsin II-like photoproduct FTIR-difference spectra were recorded for each sample. The COS-cell rhodopsin and mutant difference spectra showed close correspondence to that of rhodopsin from disc membranes. Difference bands (rhodopsin/metarhodopsin II) at 1767/1750 cm-1 and at 1734/1745 cm-1 were absent from the spectra of mutants D83N and E122Q, respectively. Both bands were absent from the spectrum of the double mutant D83N/E122Q. These results show that Asp-83 and Glu-122 are protonated both in rhodopsin and in metarhodopsin II, in agreement with the isotope effects observed in spectra measured in 2H2O. A photoproduct band at 1712 cm-1 was not affected by either single or double replacements at positions 83 and 122. We deduce that the 1712 cm-1 band arises from the protonation of Glu-113 in metarhodopsin II.

Amino Acid Sequence↗
PubMed1993

Doctors under the knife.

With Bill Clinton's new reforms only a month away, the health-care system is on the operating table--and the doctors are under the knife. Americans have a love-hate relationship with physicians: they like the care that doctors provide but hold them to blame for the nation's health-care mess. NEWSWEEK looks at how the culture of medicine may change, assesses doctors' fears--and examines the brave new world of HMOs.

American Medical Association↗
PubMed1993

Movement of the retinylidene Schiff base counterion in rhodopsin by one helix turn reverses the pH dependence of the metarhodopsin I to metarhodopsin II transition.

The environment of the retinylidene Schiff base in bovine rhodopsin has been studied by movement of its carboxylic acid counterion from position 113 to position 117 by site-specific mutagenesis. Replacement of the counterion at position 113 by a neutral amino acid residue has been shown to produce a lowering of the Schiff base acidity constant (pKa) from > 8.5 to about 6. The aim of the present work was to change the position of the counterion without causing a significant effect on the Schiff base pKa. A triple replacement mutant (Glu113-->Ala/Ala117-->Glu/Glu122-->Gln) was designed to move the position of the counterion by one helix turn in the third putative transmembrane helix (helix C). The mutant bound 11-cis-retinal to form a chromophore with a visible absorbance maximum (lambda max) of 490 nm which was independent of pH in the range of about 5-8.5. Upon illumination under conditions in which rhodopsin was converted to the active metarhodopsin II (MII) photoproduct, the mutant was converted to a metarhodopsin I (MI)-like species (lambda max = 475 nm). Furthermore, the effect of pH on the photobleaching behavior of the mutant was the reverse of that reported for rhodopsin. In the mutant, acidic pH favored the formation of the MI-like photoproduct, and basic pH favored the formation of an MII-like photoproduct (lambda max = 380 nm). The MII-like photoproduct of the mutant pigment was able to activate the guanine nucleotide-binding protein, transducin. We conclude that the Schiff base counterion in rhodopsin can be repositioned to form a pigment with an apparently unperturbed Schiff base pKa. Furthermore, a specific amino acid residue that acts as a Schiff base proton acceptor is not strictly required for photoconversion of rhodopsin to its active MII form.

Amino Acid Sequence↗
PubMed1993

Analysis of hemolysin operons in Actinobacillus pleuropneumoniae.

Among the twelve different serotypes of Actinobacillus pleuropneumoniae, the causative agent of swine pleuropneumonia, a strongly active hemolysin I (HlyI) is produced by serotypes which are particularly virulent, and less active hemolysin II (HlyII) is produced by all serotypes except type 10. In the serotypes 1, 5a, 5b, 9, 10 and 11, which produce HlyI, the hemolysin (hly) operon consists of a structural hlyIA gene, encoding pre-HlyI, an activator gene, hlyIC, necessary for the activation of pre-Hly to active Hly, and two genes, hlyIB and hlyID, involved in Hly secretion. These genes are clustered in the order, hlyICABD. This is characteristic to RTX toxin (repeats in the structural toxin) operons. The HlyII operons in all serotypes producing HlyII consist only of the pre-HlyII-encoding gene, appA, and its activator gene, appC. The serotypes, which produce HlyII, but not HlyI, contain a truncated HlyI operon, with the promoter, hlyIB and hlyID, and a small segment of the C terminus of hlyIA. This partial HlyI operon might have been formed by deletion of hlyIC and most of hlyIA. In serotype 3, which produces HlyII, but no HlyI, and which releases only minute amounts of this Hly into the growth medium, none of the hlyI genes and consequently no Hly secretion genes were found. The above results postulate that HlyII is secreted via the products of hlyIB and hlyID, and explain the low amount of HlyII secreted by serotype 3. Cloning and analysis of the structural genes encoding pre-HlyI and pre-HlyII among the different serotypes revealed differences in the hlyIA genes which are highly similar in the serologically related serotypes 1, 9 and 11, and differ from the serotypes, 5a, 5b and 10. The hlyIIA genes, in contrast, seem to be conserved in all serotypes.

Actinobacillus pleuropneumoniae↗
PubMed1993

Molecular basis of mucopolysaccharidosis type II: mutations in the iduronate-2-sulphatase gene.

A number of mutations in the X-chromosomal human iduronate-2-sulphatase gene have now been identified as the primary genetic defect leading to the clinical condition known as Hunter syndrome or mucopolysaccharidosis type II. The mutations that are tabulated include different deletions, splice-site and point mutations. From the group of 319 patients thus far studied by Southern analysis, 14 have a full deletion of the gene and 48 have a partial deletion or other gross rearrangements. All patients with full deletions or gross rearrangements have severe clinical presentations. Twenty-nine different "small" mutations have so far been characterised in a total of 32 patients. These include 4 nonsense and 13 missense mutations, 7 different small deletions from 1 to 3 bp, with most leading to a frameshift and premature chain termination, and 5 different splice-site mutations also leading to small insertions or deletions in the mRNA. A 60 bp deletion, that results from a new donor splice-site, has been observed in five unrelated patients with relatively mild clinical phenotypes. This information will not only be useful for MPS II patient and carrier diagnosis, but also will aid in the understanding of the structure and function of iduronate-2-sulphatase, and possibly in correlating genotype with phenotype.

Gene Deletion↗
PubMed1993

HSP90 homologue from Madagascar periwinkle (Catharanthus roseus): cDNA sequence, regulation of protein expression and location in the endoplasmic reticulum.

We describe cDNAs for a HSP90 homologue from Catharanthus roseus and studies on the regulation of expression. The largest cDNA (2670 bp) coded for a protein of 817 amino acids with a calculated size of 93,491 Da and a pI of 4.61. It contained a eucaryotic secretory signal, the endoplasmic reticulum (ER) targeting and retention signal (Lys-Asp-Glu-Leu), and the HSP90 protein family signature with one conservative exchange (Asn-Lys-Asp-Ile-Phe-Leu instead of Asn-Lys-Glu-Ile-Phe-Leu). RNA blots revealed a transcript of 2.8-2.9 kb, and genomic DNA blots suggested a single gene. The expression was analysed with antiserum against a fusion protein expressed in Escherichia coli. Immunoblots revealed a protein of 93 +/- 1.5 kDa (often a doublet) only in the membrane fraction, and sucrose density gradients suggested association with the ER. The protein was constitutively expressed in C. roseus cell cultures grown at 25 degrees C, and expression was apparently unaffected by various stress conditions, such as heat, high sucrose, elicitor from Phytophthora megasperma or yeast extract. It was not detectable in young C. roseus plants at room temperature, and heat shock for several hours at 37 degrees C was necessary to obtain detectable expression. In maize (Zea mays), a cross-reacting protein was detectable in cell cultures, but not in young plants. The results suggested that the cloned protein is not a major component in the heat shock response. We propose a chaperone role in the assembly and processing of cell wall components and other secreted proteins, i.e. functions that are very active in cells with a high rate of growth and division.

Amino Acid Sequence↗
PubMed1993

Molecular analysis in patients with mucopolysaccharidosis type II suggests that DXS466 maps within the Hunter gene.

Hunter disease is an X-linked mucopolysaccharidosis caused by deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS). Using the IDS cDNA and DNA probes corresponding to loci flanking the IDS locus, we performed molecular genetic studies in two patients with Hunter syndrome. An interstitial deletion spanning the middle part of the IDS gene was found in the first patient. The second patient carries a gross gene rearrangement that can be detected after HindIII or EcoRI digestion of genomic DNA, and is similar to that found recently in seven unrelated Hunter patients. Our data suggest that the structural aberration observed is a partial intragenic inversion. As the same altered hybridization pattern is also revealed by the recently described anonymous DNA probe II-10, which recognizes a frequent TaqI restriction fragment length polymorphism at the DXS466 locus, we conclude that DXS466 maps within the IDS gene, probably in an intron.

Blotting, Southern↗
PubMed1993

An evaluation of 4% prilocaine and 3% mepivacaine compared with 2% lidocaine (1:100,000 epinephrine) for inferior alveolar nerve block.

The purpose of this study was to measure the degree of anesthesia obtained with 4% prilocaine and 3% mepivacaine compared with 2% lidocaine (1:100,000 epinephrine) for inferior alveolar nerve block. Using a repeated measures design, 30 subjects randomly received an inferior alveolar injection using masked cartridges of each solution at three successive appointments. The first molar, first premolar, lateral incisor, and contralateral canine (control) were blindly tested with an Analytic Technology pulp tester at 3-min cycles for 50 min. Anesthetic success was defined as no subject response to the maximum output of the pulp tester (80 reading) within 16 min and maintenance of this reading for 50 min. Although subjects felt numb subjectively, anesthetic success as defined here occurred in 43 to 63% of the molars, in 53 to 67% of the premolars, and in 30 to 37% of the lateral incisors. No statistically significant differences in onset, success, or failure were found among the solutions. We conclude that the three preparations are equivalent for an inferior alveolar nerve block of 50-min duration.

Adult↗
PubMed1993

[The effect of oligosaccharides on piglets].

Into the starter of weaned piglets 1% lactitol and 0.2% fructo-, isomalto- or galacto-oligosaccharides were added. After an adaptation period of two weeks the piglets were slaughtered 3 hours postprandial. Compared with control animals in the trial groups urea concentrations in the serum and fermentations in the stomach were lowered, stomach emptying rates increased. Higher volumes and contents were measured in the colon, especially in the upper half, and more lactic acid.

Animal Feed↗