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Biomedical subjects

F X Schmid

Publications and source records attributed to F X Schmid.

At least 127 records · Page 7Linked to original sources
PubMed1989

Anatomically corrected malposition of the great arteries, inflow ventricular septal defect, and subaortic stenosis: diagnostic and operative implications.

Intracardiac correction of the combination of rare congenital heart lesion of anatomically corrected malposition of the great arteries, severe muscular as well as fibrous subaortic stenosis, and ventricular septal defects in the inflow and the trabecular septum in a 2 1/2 years old boy is reported. There was an additional large secundum atrial septal defect. The operation consisted of resection of the subaortic stenosis by a combined transatrial and transaortic approach, thereby regaining a wide outflow tract of the systemic ventricle. Both the ventricular and atrial septal defects were closed with Dacron patches. Reinvestigation 10 days after the operation revealed a residual pressure gradient across the outflow of the systemic ventricle of less than 10 mmHg. A secondary ventricular septal defect was detected in the anterior muscular septum at the same time and closed with a patch in a reintervention. At discharge from the hospital two weeks later the child was in excellent condition and had a stable sinus rhythm. The preoperative differential diagnosis of a double outlet right ventricle with L-malposition of the aorta as well as possible surgical approaches are discussed.

Angiocardiography↗
PubMed1989

Urgent indications for surgery in primary or secondary cardiac neoplasm.

Ten patients underwent resection of primary or secondary cardiac tumor. Two-dimensional transthoracic echocardiography per se accurately located the endoluminal cardiac mass in nine patients, and transesophageal echocardiography demonstrated a right atrial tumor in the tenth case. The indications for urgent surgery included prior embolic events (3 cases), syncopal attacks (2) or echocardiographic evidence of a multilobulated mass (2 cases). The operative strategy was standardized for atrial tumors, but for malignant myocardial neoplasm both the anatomic site and the extent of tumor growth determined the surgical procedure. Histologic examination showed myxoma in seven cases, fibroma in one and metastases of malignant melanoma in two cases. The course after resection of endoluminal benign tumor was uneventful apart from transient atrial fibrillation in four cases. Follow-up echocardiography (after 4-28 months) showed no recurrent growth. In both cases of intracardiac metastases there was recurrence within 6 to 8 months after resection of the growth.

Adult↗
PubMed1988

The stability of yeast invertase is not significantly influenced by glycosylation.

Yeast invertase exists in two different forms. The cytoplasmic enzyme is nonglycosylated, whereas the external invertase contains about 50% carbohydrate of the high mannose type. The protein moieties of both enzymes are identical. The two invertases have been used previously as a model system to investigate the influence of covalently linked carbohydrate chains on the stability of large glycoproteins, and controversial results were obtained. Here, we measured thermal and denaturant-induced unfolding by various probes, such as the loss of enzymatic activity, and by the changes in absorbance and fluorescence. The ranges of stability of the two invertases were found to be essentially identical, indicating that the presence of a high amount of carbohydrate does not significantly contribute to the stability of external invertase. Earlier findings that invertase is stabilized by glycosylation could not be confirmed. The stability of this glycoprotein is apparently determined by the specific interactions of the folded polypeptide chain. Unlike the glycosylated form, the carbohydrate-free invertase is prone to aggregation in the denatured state at high temperature and in a partially unfolded form in the presence of intermediate concentrations of guanidinium chloride.

Enzyme Stability↗
PubMed1988

Effect of glycosylation on the mechanism of renaturation of invertase from yeast.

N-Glycosylation occurs cotranslationally as soon as the growing polypeptide chain enters the endoplasmic reticulum, before the final native-like folded state is reached. We examined the role of the carbohydrate chains in the mechanism of protein folding. The in vitro folding and association of yeast invertase are used as an experimental system. External invertase contains approximately 50% carbohydrate, whereas cytoplasmic invertase is not glycosylated. The functional native state of both proteins is a homodimer. At pH greater than or equal to 6.5 and at protein concentrations below 3 micrograms/ml, the kinetics of reactivation and the final yields are similar for the two invertases. For both proteins, reactivation is a sequential reaction with a lag phase at the beginning. The nonglycosylated protein tends to aggregate during reactivation at low pH and at protein concentrations above 3 micrograms/ml. After separation of inactive material, the renatured protein is indistinguishable from the original native state by a number of physicochemical and functional criteria. The results suggest that the carbohydrate moiety does not affect the mechanism of folding and association of invertase. However, glycosylation improves the solubility of unfolded or partially folded invertase molecules and hence leads to a suppression of irreversible aggregation. Such a protective effect may also be important for the in vivo maturation of nascent glycosylated protein chains.

Circular Dichroism↗
PubMed1988

Protein-disulphide isomerase and prolyl isomerase act differently and independently as catalysts of protein folding.

Two enzymes are now known that catalyse slow steps in protein folding. Peptidyl-prolyl cis-trans isomerase catalyses the cis-trans isomerization of Xaa-Pro peptide bonds in oligopeptides and during the refolding of several proteins. The other enzyme, protein-disulphide isomerase, accelerates the reactivation of reduced proteins, presumably by catalysis of thiol-disulphide exchange reactions. Recent evidence indicates that the beta-subunit of prolyl 4-hydroxylase, an enzyme involved in collagen biosynthesis, is identical with disulphide isomerase. On the basis of this important finding, it was suggested that disulphide isomerase accelerates protein folding, not by 'reshuffling' incorrect disulphide bonds, but in the same way as prolyl isomerase by catalysing proline isomerization which is known to be important for the folding of collagen and other proteins. Here we show that the catalytic activities of these two enzymes are different. Disulphide isomerase accelerates the reformation of native disulphide bonds during protein reoxidation. We find no evidence that this enzyme can catalyse the isomerization of proline peptide bonds, a reaction efficiently accelerated by prolyl isomerase. When both enzymes are present simultaneously during protein folding, they act independently of one another.

Amino Acid Isomerases↗
PubMed1987

The mechanism of folding of pancreatic ribonucleases is independent of the presence of covalently linked carbohydrate.

The role of asparagine-linked oligosaccharides for the mechanism of protein folding was investigated. We compared the stability and folding kinetics for two sets of pancreatic ribonucleases (RNases) with identical amino acid sequences and differences in glycosylation. First the folding of RNases A (carbohydrate free) and B (a single N-linked oligosaccharide) from bovine pancreas was investigated. The kinetics of refolding were identical under a wide range of conditions. The rate of unfolding by guanidinium chloride was decreased in RNase B. In further experiments the folding of porcine RNase (three carbohydrate chains at Asn-21, -34, and -76) was compared with the corresponding data for the deglycosylated protein. Even for this RNase with almost 40% carbohydrate content the mechanism of refolding is independent of glycosylation. Although the folding mechanism is conserved, the rates of individual steps in folding are decreased about 2-fold upon deglycosylation. We interpret this to originate from a slight destabilization of folding intermediates by carbohydrate depletion. In control experiments with nonglycosylated bovine RNase A it was ascertained that treatment with HF (as used for deglycosylation) did not affect the folding kinetics. The in vitro folding mechanism of glycosylated RNases apparently does not depend on the presence of N-linked oligosaccharide chains. The information for the folding of glycoproteins is contained exclusively in the protein moiety, i.e. in the amino acid sequence. Carbohydrate chains are attached at chain positions which remain solvent exposed. This ensures that the presence of oligosaccharides does not interfere with correct folding of the polypeptide chain.

Animals↗
PubMed1987

[Assessment of heart valve reconstructive measures using intraoperative transesophageal contrast echocardiography].

In 30 patients (6 mitral stenoses, 13 mitral insufficiencies, 12 tricuspid insufficiencies) intraoperative transoesophageal contrast echocardiography (TEE) was performed to examine the valve function after AV valve reconstruction. In the beating heart 1 ml of contrast medium was injected into the ventricle to assess the success of valve reconstruction by the extent of regurgitation into the left or right atrium respectively. In all 12 patients successful tricuspid valve reconstruction was detected. In 16/19 cases with mitral valve repair successful reconstruction has been demonstrated. In another 3 patients severe mitral insufficiency after valve repair was detected by TEE, finally intraoperative decision for valve replacement was made.

Echocardiography↗
PubMed1987

Intraoperative evaluation of reconstruction of the atrioventricular valves by transesophageal echocardiography.

In a total of 30 operations the mitral valve was reconstructed in 18, the tricuspid valve in 11, and both AV-valves in one patient. The result of reconstruction was tested first in the open arrested heart by injection of crystalloid solution into the appropriate ventricle either through the reconstructed valve or one of the great arteries. Upon termination of cardiopulmonary bypass the valve function was examined in the beating heart by means of transesophageal contrast echocardiography (TEE). For visualization 0.5-1.0 cc of agitated Gelifundol was injected into the ventricle. In 22 patients open testing as well as echocardiographic visualization showed identical and good operative results. In 6 patients TEE revealed mild insufficiency, but no further surgery was done. In three patients with mitral valve repair, contrast-echocardiography showed severe insufficiency, which had not been detected during cardiac arrest. In these patients changes in the level of the subvalvular apparatus caused systolic dislocation of the leaflets and massive reflux. Because of these findings definive valve replacement was performed in the same operation. Intraoperative TEE is a simple, safe and reliable method für assessment of AV-valve repair, thereby motivating the surgeon towards valve preservation and improving the outcome of valve surgery.

Adult↗
PubMed1987

Double inlet left ventricular main chamber, subaortic small left sided right ventricle and interrupted aortic arch type A. What operation is indicated when?

A case of a 23 year old female patient who suffered from the complex congenital heart lesion of a double inlet left ventricular main chamber, subaortic small left sided right ventricle and interrupted aortic arch type A is reported. With equally high blood pressures, the perfusion in the upper half of the body was maintained through the ascending aorta while the lower half and the lungs were supplied through the pulmonary artery and a patent ductus arteriosus (PDA). Angiographically, the bulbo-ventricular foramen appeared to be nonrestrictive. However, distinct signs of muscular subaortic stenosis were detected. The hemodynamic status principally allowed surgical correction when this became necessary because of increasing left heart failure. Treatment for this complex lesion undoubtedly required reduction of pulmonary perfusion, even when associated with the danger of increasing cyanosis. Various forms of surgical treatment (functional correction, palliative procedures) were discussed. The most elegant was performed without cardiopulmonary bypass: this consisted in connection of the pulmonary artery with the descending aorta using a 16 mm Dacron tube, reconstruction of the aortic arch by a prostheso-subclavian synthetic graft, suture ligation of the PDA, and banding of the pulmonary artery trunk distal to the origin of the prosthesis. One year after the operation, the patient's physical performance has improved. Moreover, despite the disappearance of cardiac failure she has not become more cyanotic during exertion.

Adult↗
PubMed1987

[Cavernous hemangioma of the mediastinum].

After presenting an own case of a cavernous hemangioma of the mediastinum, the clinical pattern, differential diagnosis, diagnostic procedure (computed tomography), and therapy of this rare tumor form are described.

Diagnosis, Differential↗
PubMed1986

Folding mechanism of porcine ribonuclease.

The kinetics of unfolding and refolding of porcine ribonuclease were investigated. The unfolded state of this protein was found to consist of a fast-refolding species (UF) and two slow-refolding species (UIS and UIIS). After the rapid collapse of the structure during the N (native)----UF unfolding reaction, UIS and UIIS are produced from UF by two independent slow isomerizations of the unfolded polypeptide chain, leading ultimately to a mixture of about 10% UF, 20% UIIS and 70% UIS molecules at equilibrium. This is at variance with all other ribonucleases investigated to date, which show a distribution of 20% UF, 60 to 70% UIIS and only 10 to 20% UIS. The two isomerizations of the unfolded porcine protein differ strongly in rate. The first process with tau = 250 seconds (10 degrees C) leads to an increase in the fluorescence of Tyr92 and was identified as cis in equilibrium trans isomerization of Pro93. At equilibrium, most unfolded molecules contain an incorrect trans Pro93. The second isomerization is much slower (tau = 1300 s at 10 degrees C) and leads to a predominance of the incorrect isomer as well. Like isomerization of Pro93, it is governed by an activation enthalpy of 22 kcal/mol (92 kJ/mol) and it was tentatively assigned to the Pro114-Pro115 sequence of porcine ribonuclease. Because of the wide separation in rate between the two reactions, molecules with an incorrect isomer only at Pro93 accumulate transiently after unfolding. These are the UIIS molecules. Most of them are finally converted to UIS by the 1300 second process. All molecules that have undergone this isomerization refold very slowly, i.e. the UIS molecules. The major fraction contains two incorrect isomers. A 1300 second isomerization after unfolding and a predominant very slow refolding reaction were observed only for the porcine protein. We suggest that these changes in the folding mechanism may be correlated with the presence of the Pro114-Pro115 sequence, which occurs only in porcine ribonuclease. The refolding pathway of porcine UIIS involves the rapid formation of a native-like intermediate with an incorrect trans Pro93 as was found previously for the bovine ribonuclease, where the UIIS species predominates in the unfolded state.

Animals↗
PubMed1986

Use of a trypsin-pulse method to study the refolding pathway of ribonuclease.

Trypsin pulses, applied after varying times of refolding, have been employed to probe the accessibility of the polypeptide chain of ribonuclease A during the process of refolding. The increase in resistance against proteolytic cleavage was measured by activity assays and by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The sites of cleavage which become inaccessible in the course of refolding are located in the 31 - 39 chain segment of the ribonuclease chain. Protection of this region against attack by trypsin is attained on the major slow refolding pathway in parallel with the formation of a native-like folded, active intermediate, when refolding is carried out under conditions which strongly stabilize the folded state. Under conditions of marginal stability intermediates are not observed during refolding and the formation of trypsin-resistant molecules occurs with the same kinetics as the generation of native ribonuclease. In the native protein the 31 - 39 region of the ribonuclease chain largely forms a loop structure, which is located at the surface of the molecule. Our results indicate that this part of the sequence is still accessible at early stages of refolding, when a hydrogen-bonded network is formed. It is structured and hence does not become inaccessible until the formation of the overall folded native or native-like structure. This suggests that the 31 - 39 region of the ribonuclease chain is not important for early steps which direct the pathway of refolding.

Electrophoresis, Polyacrylamide Gel↗
PubMed1986

Folding kinetics of mammalian ribonucleases.

The folding kinetics of seven different pancreatic ribonucleases are compared both under native conditions and within the unfolding transition. In general, the folding kinetics of these proteins are similar despite numerous amino acid substitutions. Ribonucleases with 4-6 proline residues show 80% slow-folding species. For three ribonucleases with 7 prolines this number increases to 90%. Porcine ribonuclease with a unique Pro 114-Pro 115 sequence folds significantly slower than other ribonucleases which do not show this sequence.

Amino Acid Sequence↗
PubMed1986

Proline isomerization during refolding of ribonuclease A is accelerated by the presence of folding intermediates.

The trans----cis isomerization of Pro 93 was measured during refolding of bovine ribonuclease A. This isomerization is slow (tau = 500 s) under marginally stable folding conditions of 2.0 M GdmCl, pH 6, at 10 degrees C. However, it is strongly accelerated (tau = 100 s) in samples which, prior to isomerization, had been converted to a folding intermediate by a 15 s refolding pulse under strongly native conditions (0.8 M ammonium sulfate, 0 degree C). The results demonstrate that extensive folding is possible before Pro 93 isomerizes to its native cis state and that the presence of structural folding intermediates leads to a marked increase in the rate of subsequent proline isomerization.

Isomerism↗
PubMed1986

Role of proline peptide bond isomerization in unfolding and refolding of ribonuclease.

The isomerization of the proline peptide bond between tyrosine-92 and proline-93 in bovine pancreatic ribonuclease A has been investigated in the unfolded protein as well as during the slow refolding process. This bond is in the cis state in the native protein. By comparison of various homologous ribonucleases we show that isomerization of proline-93 is associated with a change in fluorescence of tyrosine-92. This provides a spectroscopic probe to monitor this process in the disordered chain after unfolding as well as its reversal in the course of slow refolding. In unfolded ribonuclease incorrect trans isomers of proline-93 are found in both slow-folding species. trans----cis reversal of isomerization of this proline peptide bond during refolding shows kinetics that are identical with the time course of formation of native protein. Isomerization of proline-93 is slower than the formation of a native-like folded intermediate that accumulates on the major slow refolding pathway. Models to explain these results are discussed.

Animals↗
PubMed1985

Native-like folding intermediates of homologous ribonucleases.

The mechanism of the slow refolding reactions of four different pancreatic ribonucleases from ox, sheep, red deer, and roe deer has been investigated. Refolding kinetics of these proteins were very similar. In particular, a native-like intermediate, IN, was shown to be populated on the slow refolding pathway of all ribonucleases. We conclude that, similar to the stability of the folded proteins, the pathway of slow refolding has been conserved despite the differences in amino acid sequence and the varying number of proline residues.

Animals↗
PubMed1984

Tests of the simple model of Lin and Brandts for the folding kinetics of ribonuclease A.

L.-N. Lin and J.F. Brandts recently proposed a simple model for the folding kinetics of ribonuclease A in which folding intermediates are not detectable. We have tested the basic assumption of the simple model for the major unfolded species, which is produced by a slow isomerization (the "X in equilibrium Y reaction" according to Lin and Brandts) after unfolding. The simple model assumes that in refolding the slow Y----X reaction must occur before any folding can take place. We have measured the Y----X reaction during folding. Tyrosine-detected folding occurs before the Y----X reaction; the difference in rate between the Y----X reaction and folding monitored by tyrosine absorbance becomes large when the stabilizing salt 0.56 M (NH4)2SO4 is added. The simple model predicts that the kinetic properties of the X in equilibrium Y reaction in unfolded ribonuclease are the same as those of tyrosine-detected folding. We find, however, that the kinetics of the X in equilibrium Y reaction in unfolded ribonuclease are independent of urea concentration, whereas the rate of tyrosine-detected folding decreases almost 100-fold between 0.3 and 5 M urea, as reported by Lin and Brandts. We point out that the kinetic properties of the X in equilibrium Y reaction in unfolded ribonuclease are characteristic of proline isomerization.

Kinetics↗