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Biomedical subjects

H Thrum

Publications and source records attributed to H Thrum.

At least 19 recordsLinked to original sources
PubMed2001

Stability after medial collateral ligament release in total knee arthroplasty.

Six knees from cadavers were tested for change in stability after release of the medial collateral ligament with posterior cruciate-retaining and substituting total knee replacements. Load deformation curves of the joint were recorded in full extension and 30 degrees, 60 degrees, and 90 degrees flexion under a 10 N-m varus and valgus torque, 1.5 N-m internal and external rotational torque, and a 35 N anterior and posterior force to test stability in each knee. The intact specimen and posterior cruciate ligament-retaining total joint replacement were tested for baseline comparisons. The superficial medial collateral ligament was released, followed by release of the posterior cruciate ligament. The knee then was converted to a posterior-stabilized implant. After medial collateral ligament release, valgus laxity was statistically significantly greater at 30 degrees, 60 degrees, and 90 degrees flexion after posterior cruciate ligament sacrifice than it was when the posterior cruciate ligament was retained. The posterior-stabilizing post added little to varus and valgus stability. Small, but significant, differences were seen in internal and external rotation before and after posterior cruciate ligament sacrifice. The posterior-stabilized total knee arthroplasty was even more rotationally constrained in full extension than the knee with intact medial collateral ligament and posterior cruciate ligament.

Arthroplasty, Replacement, Knee↗
PubMed1986

Self-resistance of the nourseothricin-producing strain Streptomyces noursei.

The nourseothricin producer Streptomyces noursei is resistant to its own antibiotic in submerged as well as in surface culture. The strain shows no cross-resistance to miscoding inducing aminoglycoside antibiotics. Cell free extracts of Streptomyces noursei inactivate nourseothricin by enzymatic acetylation. The pattern of cross-resistance of Streptomyces noursei correlates well with the substrate specificity of the nourseothricin acetyltransferase. Furthermore, the acetyltransferase activity parallels the resistance level in nourseothricin-producing strains and nonproducing mutants. The results suggest that the nourseothricin acetyltransferase is important in the self-defence strategy of the nourseothricin-producing strain.

Acetyltransferases↗
PubMed1985

Roflamycoin--a new channel-forming antibiotic.

Ion permeability of lipid bilayers was studied in the presence of a new antifungal pentaene antibiotic, roflamycoin, the structure of which differs considerably from that of the well-known polyene channel-former amphotericin B. Both of them, however, show the property of increasing the membrane permeability only in the case of sterol-containing membrane when added on both its sides. The conductance is strongly dependent on the concentration of the antibiotic in the solutions and of sterol in the membrane. Unlike the amphotericin B channels, roflamycoin channels are potential-dependent and have short lifetime (approx. 1 s) and high conductance (approx. 100 ps in 1 M KCl), which increases linearly with the salt concentration and is not blocked by the familiar blockers of amphotericin B channels. The two antibiotics seem to have a common mechanism of channel formation, viz. the formation starts from two semi-pores assembled in the opposite monolayers from several molecules of the antibiotic and sterol. However, the inner diameter of the roflamycoin channel is larger because of the different antibiotic-to-sterol ratio in the channel aggregate. It is believed that the difference in the ratio is due to the presence of the methyl group in the polyene chain of roflamycoin, and the considerable difference in lifetimes of the two types of channels depends on the terminal groups of the antibiotics.

Amphotericin B↗
PubMed1985

Bacterial resistance to streptothricins.

Resistance to streptothricin was studied in bacteria with different resistance mechanisms. The laboratory-induced streptothricin-resistant mutant E. coli A19 Stcr 2/2/1 showed a high level of cross-resistance to aminoglycosides and other miscoding inducing antibiotics. In contrast, aminoglycosid-resistant E. coli strains with plasmid-determined aminoglycoside modifying enzymes were sensitive to streptothricin. Enzymatic inactivation of streptothricin by acetylation was demonstrated for the streptothricin producing Streptomyces noursei, strain NG13. This strain showed no cross-resistance to miscoding inducing aminoglycosides.

Acetylation↗
PubMed1985

Microbial conversion of daunorubicin into N-acetyl-13(S)-dihydrodaunomycin and bisanhydro-13-dihydrodaunomycinone.

By using a strain of Streptomyces willmorii, daunorubicin (daunomycin) was stereoselectively converted into N-acetyl-13(S)-dihydrodaunomycin and bisanhydro-13-dihydrodaunomycinone. The absolute stereochemistry of the new chiral center in N-acetyl-13(S)-dihydrodaunomycin was established by means of nuclear Overhauser effect measured in the 9,13-O-isopropylidene derivative.

Daunorubicin↗
PubMed1980

Counterion dependent variation of DNA secondary structure in (A . T) clusters: evidence by use of netropsin as a structural probe.

The interaction of the oligopeptide antibiotic netropsin (Nt) with (A . T) regions of DNA is characterized by a spectrum of discrete modes. This has been revealed by viscometric analysis, at 20 degrees C and 0.2 M "counterions", for NaDNA in a preceding and for NH4DNA in this paper. The increase of DNA contour length as induced by one Nt molecule was found to depend on the special mode only, while the respective stiffening is generally higher for NH4DNA. The latter property is interpreted in terms of an enhanced flexibility, relative to that of NaDNA, of the (A . T) cluster segments before complex formation. For some of the interaction modes of the DNA-Nt systems a difference in the number of corresponding binding sites has been observed. This phenomenon is understood by assuming an influence of the counterion species upon existing equilibria between different forms of the (A . T) cluster secondary structure. Not less than 5 to 10% of the total DNA are effected in this manner. Upper limits for the local differences in the axial rise per base pair are 0.04 nm and 0.02 nm.

Animals↗
PubMed1980

Regulative influence of o-aminobenzoic acid (OABA) on the biosynthesis of nourseothricin in cultures of Streptomyces noursei JA 3890b. V. Effect of OABA on cytochrome levels and amino acid transport.

o-Aminobenzoic acid (OABA) known by its stimulatory effect on streptothricin biosynthesis by Streptomyces noursei JA 3890b was found to suppress specifically the formation of cytochrome a-type terminal oxidase while the levels of the b- and c-type cytochromes apparently remained unaffected. This change was coupled to decreased capacity of transport of u-14C-L-alanine and u-14C-L-glutamic acid into the mycelium, giving rise to delay of amino acid catabolism and decreased production of nitrogen catabolites within the cell. The above results provide supporting evidence for conjectures recently published by us concerning the control by nitrogen catabolites of the secondary metabolism of this strain. As a summary a scheme is proposed showing several hypothetic mechanisms by which nitrogen catabolite regulation of nourseothricin production could be accomplished.

Amino Acids↗
PubMed1980

Isolation and structures of nitrogen-free platenolide glycosides. I. The 5-O-(deoxy-3'-C-acetyl-beta-D-hexopyranosyl)-platenolides I and II.

Four novel nitrogen-free glycosides of platenolides I and II were isolated as secondary shunt metabolites of the turimycin biosynthesis from the culture broth of an industrial strain of Streptomyces hygroscopicus IMET JA 6599. By spectral (MS, 1H and 13C NMR) studies the structures of the glycosides have been settled as 5-O-(4',6'-dideoxy-3'-C-acetyl-beta-D-hexopyranosyl)-platenolide I (DDAH-Pl-I), 5-O-(4',6'-dideoxy-3'-C-acetyl-beta-D-hexopyranosyl)-platenolide II (DDAH-Pl-II), 5-O-(4',6'-dideoxy-3'-C-acetyl-beta-D-hexopyranosyl)-14-hydroxyl-platenolide II (DDAH-OH-Pl-II) and 5-O-(6'-deoxy-3'-C-acetyl-beta-D-hexopyranosyl)-platenolide II (DAH-Pl-II). A fifth glycoside, 5-O-(6'-deoxy-3'-C-acetyl-beta-D-hexopyranosyl)-platenolide I (DAH-Pl-I) was identified through its MS data.

Anti-Bacterial Agents↗
PubMed1980

Isolation and structures of nitrogen-free platenolide glycosides. II. The 5-O-(alpha-mycarosyl)- and 5-O-(3'-demethyl-beta-mycaroxyl)-platenolides I and II.

Three novel glycosides of platenolides I and II containing either mycarose (2,6-dideoxy-3-C-methyl-L-ribohexopyranose) or 3-demethyl-mycarose (2,6-dideoxy-L-ribohexopyranose) were isolated as the shunt products of turimycin biosynthesis by an industrial strain of Streptomyces hygroscopicus IMET JA 6599. By means of MS, 13C and 1H NMR spectroscopic studies, their structures were assigned as 5-O-(alpha-mycarosyl)-platenolide I (MYC-Pl-I), 5-O-(alpha-mycarosyl)-platenolide II (MYC-Pl-II) and 5-O-(3'-demethyl-beta-mycarosyl)-platenolide II (DM-MYC-Pl-II). The occurrence of 3-demethyl-mycaroside amongst the shunt metabolites is discussed in terms of its biosynthesis.

Acetylation↗
PubMed1980

Action of streptothricin F on ribosomal functions.

The effect of streptothricin F on elongation factor-dependent and on elongation factor-free translation systems was studied. Streptothricin F inhibits factor-dependent as well as factor-free polypeptide synthesis. The results suggest that streptothricin F inhibits polypeptide synthesis via interaction with the ribosome. In partial reactions streptothricin F impairs EF-G-dependent translocation and to a lesser extent EF-Tu-dependent binding of aa-RNA to the ribosome, while it does not affect peptide bond formation significantly.

Anti-Bacterial Agents↗