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Biomedical subjects

V Horn

Publications and source records attributed to V Horn.

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

Fusion of trpB and trpA of Escherichia coli yields a partially active tryptophan synthetase polypeptide.

The separate alpha and beta polypeptides of the tryptophan synthetase of bacteria are represented in fungi by a fusion polypeptide in which the first third is homologous to bacterial alpha chains and the remainder is homologous to bacterial beta chains. In the yeast polypeptide, a short nonhomologous "connector" joins the two homologous segments. The chromosomal order of all bacterial genes that specify tryptophan synthetase beta and alpha chains, respectively, is trpB-trpA. Fusion of these genes in their present arrangement would result in the synthesis of a polypeptide with a segmental order, N-beta-alpha-C, opposite that observed in fungi. To investigate possible explanations for the apparent transposition that occurred in the evolution of the fungal gene we have made two fusions of trpB and trpA of Escherichia coli in their natural orientation. We find that the fusion proteins are synthesized but both are less active catalytically than the wild type bacterial protein. In addition, the fusion proteins associate abnormally, they are activated only slightly by wild type alpha or beta 2, and they are less sensitive than the wild type protein to inhibition by antibodies to alpha or beta 2. The fusion proteins have normal substrate affinities. Our findings suggest that the altered structures of the fusion proteins affect catalytic ability and the locations of the alpha and/or beta chain combining sites. This structural distortion may have prevented the natural selection of direct gene fusions during the course of the fungal gene's evolution.

Base Sequence↗
PubMed1985

The influence of the pH value of the synovial fluid on the articular cartilage in rabbits. A scanning electron microscopic study.

After the intraarticular injection of isoosmolaric buffer solutions with pH values of 4.0 and 10.0 or 7.3 (control side) into the knee joints of rabbits the appearance of a fibrillated network on a plane parallel to the surface and tears in the articular cartilage are seen with the aid of scanning electron microscopy. The results are interpreted as a damage of the superficial layer of the articular cartilage. In a long-term follow up only the growing rabbits are able to repair these lesions, the adult animals are not capable to do it.

Animals↗
PubMed1984

The submicroscopic structure of a chondroblastic osteogenic sarcoma.

Two patients are reported with a chondroid form of osteosarcoma, whose structure was also analyzed submicroscopically. The clinical and radiologic picture and the rapid lethal progress of the disease indicated an osteosarcoma, while both histologic and electron-microscopic investigation suggested the prevalence of malignant chondroid. Progress in the treatment of osteosarcoma makes it essential for diagnostic, therapeutic and prognostic reasons to reintroduce subclassification of these tumors in an attempt to correlate their morphological picture with their biologic properties. According to our experience to date, it seems that the cartilaginous component in no way ameliorates the rapid malignant penetration of the osteosarcoma. It is essential to distinguish these tumors from the usually much less malignant chondrosarcomas and to place the chondroblastic osteogenic sarcoma among in spite of the clear predominance of the malignant chondroid, and thus also introduce highly radical and combined therapy.

Adolescent↗
PubMed1984

Repression is relieved before attenuation in the trp operon of Escherichia coli as tryptophan starvation becomes increasingly severe.

Expression of the tryptophan operon of Escherichia coli is regulated over about a 500- to 600-fold range by the combined action of repression and attenuation. Repression regulates transcription initiation in response to variation in the intracellular concentration of tryptophan. Attenuation regulates transcription termination at a site in the leader region of the operon in response to changes in the extent of charging of tRNATrp. We measured repression independently of attenuation to ascertain whether these regulatory mechanisms were used differentially by the bacterium as the severity of tryptophan starvation was increased. We found that repression regulated transcription of the operon over the range from growth with excess tryptophan to growth under moderate tryptophan starvation. By contrast, attenuation (termination control) was not relaxed until tryptophan starvation was in the moderate-to-severe range. Thus, attenuation and repression were used to regulate transcription in response to different degrees of tryptophan deprivation. Consistent with this conclusion is the observation that when tryptophan starvation was sufficient to relieve repression 50 to 60%, 65% of the tRNATrp of the bacterium was charged. These findings provide a possible explanation for the existence of only two tryptophan codons in the coding region for the trp leader peptide of Enterobacteriaceae.

Bacteriophage lambda↗
PubMed1984

A biological and morphological comparison of cartilage cells in various kinds of lesions.

Cartilage is an important tissue, biologically and morphologically intermediate between connective tissue and bone. Much of the current knowledge on the biology of cartilage is still hypothetical, particularly that on the reproduction of mature cartilage cells. The existence of cartilage, and its formation, are dependent on certain conditions of metabolism, which for the most part differ strongly from those under which connective tissue or bone are produced, though these tissues are often closely related morphologically. One of the greatest problems in this field of human pathology is the total lack of correspondence between the micromorphology of most cartilaginous tumours and their biological properties, especially malignant proliferation. Thus cartilage lesions, particularly cartilaginous tumours, call for special, often unconventional methods, for even a superficial assessment. It appears that for evaluation of especially the biological properties of cartilage cells, the submicroscopic appearance of the nucleus is of special importance. A suitable model for the study of biological and morphological correlations of cartilage is the ossification of the cartilaginous skeleton, the appearance and existence of cartilage-cells in tissue cultures, and the behaviour of cartilaginous tissue under specific biomechanical conditions.

Bone and Bones↗
PubMed1984

The calcified-noncalcified cartilage interface: the tidemark.

Tidemark is an interface which may better be defined by biochemical methods than by morphology. It originates, by chondrocyte activity, between calcified and noncalcified cartilage layers of any kind, hyaline or fibrous, in areas exposed to either loading (joint) or pulling (insertion). In the articular cartilage it appears with skeletal maturation, in other localizations it is age-independent. It should be regarded as a special instance of a broader phenomenon of the calcification/mineralization front. Inside the joint cartilage its changes reflect the slow remodelling of the calcified layer and its inapparent shift towards the surface of the articular cartilage. In the marginal transitional zone of the joint, tidemark smoothly passes into the periosteum. Chondrocytes on both sides of the tidemark are positive for alkaline phosphatase and the positive reaction continuously goes on to the periosteum.

Adolescent↗