Biomedical subjects

R Heupel

Publications and source records attributed to R Heupel.

3 recordsLinked to original sources

PubMed1994

Protein organization in the matrix of leaf peroxisomes. A multi-enzyme complex involved in photorespiratory metabolism.

This report is an investigation on how the compartmentation of peroxisomal metabolism, involved in the photorespiratory cycle, is accomplished. With isolated peroxisomes from spinach leaves the conversion of serine to glycerate, as coupled to the conversion of glycolate to glycine, was measured. Not only with intact but also with osmotically shocked peroxisomes, which had retained the aggregated state of the peroxisomal matrix but lost the integrity of the boundary membrane, the rates of glycerate synthesis were as high as required for the photorespiratory cycle in vivo. With both intact and shocked peroxisomes the intermediates glyoxylate and hydroxypyruvate did not equilibrate with the medium. It appears from these results that the apparent compartmentation of peroxisomal metabolism is not due to the function of the boundary membrane but to the organization of peroxisomal enzymes in multi-enzyme complexes. When glycolate was added to peroxisomes without transamination partners, glyoxylate was released from the peroxisomes while the peroxisomal matrix partially disintegrated. With solubilized peroxisomes a partial reconstitution of functional enzyme complexes was achieved by the addition of poly(ethylene glycol). The function of the apparently very stable peroxisomal multi-enzyme complexes in protecting the cells from the toxic intermediates H2O2 and glyoxylate is discussed.

Cell Compartmentation↗

PubMed1991

Compartmentation studies on spinach leaf peroxisomes : evidence for channeling of photorespiratory metabolites in peroxisomes devoid of intact boundary membrane.

In concurrence with earlier results, the following enzymes showed latency in intact spinach (Spinacia oleracea L.) leaf peroxisomes: malate dehydrogenase (89%), hydroxypyruvate reductase (85%), serine glyoxylate aminotransferase (75%), glutamate glyoxylate aminotransferase (41%), and catalase (70%). In contrast, glycolate oxidase was not latent. Aging of peroxisomes for several hours resulted in a reduction in latency accompanied by a partial solubilization of the above mentioned enzymes. The extent of enzyme solubilization was different, being highest with glutamate glyoxylate aminotransferase and lowest with malate dehydrogenase. Osmotic shock resulted in only a partial reduction of enzyme latency. Electron microscopy revealed that the osmotically shocked peroxisomes remained compact, with smaller particle size and pleomorphic morphology but without a continuous boundary membrane. Neither in intact nor in osmotically shocked peroxisomes was a lag phase observed in the formation of glycerate upon the addition of glycolate, serine, malate, and NAD. Apparently, the intermediates, glyoxylate, hydroxypyruvate, and NADH, were confined within the peroxisomal matrix in such a way that they did not readily leak out into the surrounding medium. We conclude that the observed compartmentation of peroxisomal metabolism is not due to the peroxisomal boundary membrane as a permeability barrier, but is a function of the structural arrangement of enzymes in the peroxisomal matrix allowing metabolite channeling.

Journal Article↗

PubMedDate not supplied

[Patellar changes during long-term observations on the Blauth knee joint endoprosthesis].

Changes in the position and structure of the patella and their importance with regard to pain patterns are described on the basis of long-term observation of the Blauth prosthesis. Examinations were performed on 206 knee prostheses on average 37.6 months (min. 12, max. 120 months) after implantation. Axial roentgenograms showed the patella to be laterally subluxated in 12% of the cases, and luxated in one. Also in 12% of the cases, osteolytic destruction of the posterior surface of the patella was found; there was a statistically significant correlation between the two groups, but they were not identical. In cases with changes in the patellar structure, initial pain on walking was significantly more frequent, though this was not so in cases where the kneecap had shifted from its normal position. The authors discuss possible connections with curvature radii and with the distances between the center of rotation and the sliding support on the femoral part of the prosthesis as causes of increased complaints in low kneecaps and for the increased incidence of structural changes in high kneecaps. The term "retropatellar pain syndrome" is applied to patients who experience pain when climbing stairs, rising from chairs and when starting to walk, in whom at least 2 of these complaints are positive: A total of 10.2% of the patients complained of considerable retropatellar pain. A patellectomy was performed in 8 of these patients. The radiological and histological analyses of 3 of the patellae removed showed evidence of arthrosis deformans at different stages, with concomitant synovitis.

Aged↗