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Biomedical subjects

T Hofmann

Publications and source records attributed to T Hofmann.

At least 91 records · Page 5Linked to original sources
PubMed1995

The amphotropic and ecotropic murine leukemia virus envelope TM subunits are equivalent mediators of direct membrane fusion: implications for the role of the ecotropic envelope and receptor in syncytium formation and viral entry.

The murine leukemia virus (MuLV) envelope protein was examined to determine which sequences are responsible for the differences in direct membrane fusion observed with the ecotropic and amphotropic MuLV subtypes. These determinants were studied by utilizing amphotropic-ecotropic chimeric envelope proteins that have switched their host range but retain their original fusion domain (TM subunit). Fusion was tested both in rodent cells and in 293 cells bearing the human homolog of the ecotropic MuLV receptor. The results demonstrate that the amphotropic TM is able to mediate cell-to-cell fusion to an extent equivalent to that mediated by the ecotropic TM, indicating that their fusion domains are equivalent. The "murinized" human homolog of the ecotropic receptor supports syncytium formation as well as the native murine receptor. These findings suggest that interactions between the ecotropic envelope protein and conserved sequences in the ecotropic receptor are the principal determinants of syncytium formation. The relationship of the fusion phenotype to pH-dependent infection and the route of viral entry was examined by studying virions bearing the chimeric envelope proteins. Such virions appear to enter cells via a pathway that is directed by the host range-determining region of their envelope rather than by sequences that confer pH dependence. Therefore, the pH dependence of infection may not reflect the initial steps in viral entry. Thus, it appears that both the syncytium phenotype and the route of viral entry are properties of the viral receptor, the amino-terminal half of the ecotropic envelope protein, or the interaction between the two.

3T3 Cells↗
PubMed1994

Respiratory allergy: hazard identification and risk assessment.

Various chemicals and proteins of industrial importance are known to cause respiratory allergy, with occupational asthma being the most important manifestation of the disease. This paper describes clinical syndromes, mechanisms associated with occupational respiratory hypersensitivity, and methods available currently for the prospective identification of potential respiratory allergens. Certain classes of chemicals are commonly associated with occupational respiratory allergy. There is insufficient information, however, to predict respiratory sensitization potential from analysis of structure alone, although reactivity with proteins is likely to be relevant. As yet there exist no fully validated or widely applied predictive methods or internationally harmonized guidelines. The most promising predictive animal methods are the mouse IgE test and guinea pig models. Work in mice has focused upon events occurring during the induction phase of sensitization following primary encounter with the test chemical. In contrast, guinea pig models have been used primarily to identify respiratory allergens (chemicals or proteins) as a function of elicitation reactions induced in previously sensitized animals. Given the possible serious health manifestations of respiratory allergy, early identification of respiratory sensitizers is urgently required. The two methods should, as a priority, be developed further and the production of a detailed protocol for these methods be undertaken to facilitate further validation. Together, this information will allow for two types of risk assessment associated with respiratory allergy: the risk that exposure to a material will (1) induce sensitization in an individual and (2) elicit allergic reactions in a previously sensitized individual.

Allergens↗
PubMed1994

Mechanism of pepsin-catalyzed aminotranspeptidation reactions.

1. The tetrapeptide Ala2-Nph2 (where Nph = p-nitrophenylalanyl) is treated by porcine pepsin to study the mechanism of aminotranspeptidation reactions. 2. The major initial product is Ala2-Nph and the major transpeptidation products are Nph2 and Nph3 accompanied by some Nph, a little Nph4, Ala2-Nph3 and Ala2-Nph4. 3. Oligomers of Nph greater than tetramers are formed near the end of the reaction. 4. In presence of [3H]Nph, no incorporation of Nph into the transpeptidation products is observed. 5. 18O-labeling shows extensive incorporation of 18O atoms from [18O]water in the carbonyl oxygens of Nph residues.

Amino Acid Sequence↗
PubMed1993

Secondary substrate binding in aspartic proteinases: contributions of subsites S3 and S'2 to kcat.

The kinetic parameters kcat and Km were determined at 25 degrees C and pH 5.5 for endothiapepsin and rhizopuspepsin acting on the series of substrates Ac-Ala(m)-Lys-Nph-Ala(n)-amide where Nph is p-nitrophenylalanine, and m and n equal 0-4. Kinetic parameters were also determined at 25 degrees C and pH 3.5 for pig pepsin acting on the series of substrates Ac-Ala(m)-Phe-Nph-Argn-Ala(n)-amide, where m equals 0 to 2 and n equals 0 or 1, and another series based on -Ile-Glu-Phe-Nph-Arg-, which is the core of a series of peptides designed by Dunn et al. (1986, Biochem. J. 237, 899-906). Km values were found to be largely independent of increases in the chain length of the substrates whereas kcat values showed large increases with increasing chain length. With endothiapepsin and rhizopuspepsin the largest increases (between 13-fold and over 150-fold) were obtained when alanine residues were added in positions P3 and P'2 and thus are similar to those observed previously with penicillopepsin. Additions of alanines to positions P2, P'3, and P'4 gave much smaller increases. In the case of pig pepsin the results were not as clearcut. Whereas the largest increases were seen for positions P3 and P'2 only with some of the peptides, the increases were strongly dependent on the length of the peptides. With some of the longer peptides the increases were comparable to those seen for positions P2 and P'3. Thus, whereas the addition of two alanines in position P3 to the dipeptide Ac-Phe-Nph-amide caused a large proportional increase in kcat, the increase was much smaller when the addition was made to the homologous tetrapeptide and even smaller when made to the pentapeptide Ac-Ala-Phe-Nph-Arg-Ala-amide. Additions of arginine in position P'2 gave large increases in kcat for all three peptides of the series.

Amino Acid Sequence↗
PubMed1993

The primary structure of carboxypeptidase S1 from Penicillium janthinellum.

The complete amino acid sequence of carboxypeptidase S1 from Penicillium janthinellium has been determined by N-terminal sequencing of the reduced and vinylpyridinated protein and of peptides obtained by cleaved with cyanogen bromide, iodosobenzoic acid, hydroxylamine, endoproteinase LysC, endoproteinase AspN and Glu-specific proteinase from B. licheniformis. The enzyme consists of a single peptide chain of 433 amino acid residues and contains 9 half-cystine residues and one glycosylated asparagine residue. A comparison to other carboxypeptidases shows that the enzyme is homologous to carboxypeptidase-Y and carboxypeptidase-MIII from malt. Specificity and binding of substrates are discussed from a three-dimensional model based on the known structure of carboxypeptidase-Y from Saccharomyces cereviciae and carboxypeptidase II from wheat.

Amino Acid Sequence↗
PubMed1993

Studies on the effects of a high dose UVA-1 radiation therapy on surface markers and function of epidermal Langerhans cells.

Recently, high-dose UVA-1 therapy (340-400 nm) was introduced as an effective treatment of severe exacerbated atopic dermatitis. Since the target of this type of radiation in the skin is not known we investigated using the mouse model whether surface markers of the antigen-presenting function of epidermal Langerhans cells are affected by UVA-1 radiation. Even repeated high doses of UVA-1 radiation (up to 50 J/cm2) had no detectable effect on surface ATPase activity and Ia antigen expression on Langerhans cells. Also, the contact allergen oxazolone was presented normally in skin treated with UVA-1 radiation. In contrast, if the mice were injected 1 h before irradiation with 8-methoxypsoralen a dramatic reduction in ATPase activity and Ia antigen expression on Langerhans cells was observed and the induction of contact sensitivity was suppressed (PUVA effect). These results show that epidermal Langerhans cells are not impaired either in structure or function and that these cells probably do not represent the primary target of UVA-1 radiation in the skin. No side effects resulting from a diminished Langerhans cell function should result from high-dose UVA-1 therapy.

Adenosine Triphosphatases↗
PubMed1993

Investigation of possible metabolism of pigment yellow 17, a 3,3'-dichlorobenzidine-based pigment, after inhalation exposure in rats.

Rats were exposed by inhalation to the technically highest administrable concentration of 230 mg Pigment Yellow 17/m3 air for 4 h. Inhalability of the dust was guaranteed by a mass-median aerodynamic diameter of 1.0-1.1 microns. For 14 days after exposure, urine and serum samples were analysed for 3,3'-dichlorobenzidine, the parent carcinogenic amine of the test compound. No 3,3'-dichlorobenzidine could be detected either in urine or blood, the detection limit being 5 ng/ml for both media. Based on the results of this study there is no evidence for metabolic cleavage of Pigment Yellow 17 to 3,3'-dichlorobenzidine in the rat.

3,3'-Dichlorobenzidine↗
PubMed1993

Detection of left-to-right shunt in atrial septal defect by negative contrast echocardiography: a comparison of transthoracic and transesophageal approach.

The occurrence of a right atrial negative contrast effect as an indicator of left-to-right shunt was studied in 101 patients with atrial septal defect by peripheral venous contrast injection during transthoracic and transesophageal echocardiography. Confirmation of the diagnosis was provided by cardiac catheterization or by autopsy in 72 (72%) patients. The defect could be visualized directly in 57 (57%) patients during the transthoracic and in 93 (93%) during the transesophageal examination (p < 0.001). A negative right atrial echo contrast effect was observed in 53 of 92 (58%) patients from the transthoracic and in 86 of 92 (93%) patients from the transesophageal approach (p < 0.001). Among these were seven (7%) patients with an aneurysmal interatrial septum but no directly visible defect during conventional transesophageal imaging. Appearance of contrast in the left atrium indicating right-to-left shunting was seen in 70 of 92 (76%) patients from the transthoracic and in 91 of 92 (99%) patients from the transesophageal approach (p < 0.001). Contrast injection during transesophageal imaging also helped identify additional malformations in 12 (12%) patients. Thus transesophageal echocardiography with echo contrast injection is a very reliable diagnostic method in patients with suspected atrial septal defect.

Adolescent↗
PubMed1993

[Transesophageal echocardiography in patients with systemic arterial embolism].

The percentage of ischemic strokes or peripheral arterial embolism attributed to cardiogenic embolism is about 30% and 75%, respectively. Diagnostic work-up in patients with prior arterial embolism is of prognostic importance, because embolic events are often recurrent. Cardioembolic sources with major risk of embolism are atrial fibrillation, mechanical or biological heart valve prosthesis, left ventricular or left atrial thrombi, left atrial myxomas, bacterial endocarditis, nonbacterial thrombotic endocarditis and nonischemic dilative cardiomyopathies. Cardioembolic sources with minor risk of embolism are mitral valve prolapse, isolated mitral annular calcification, patent foramen ovale, atrial septal aneurysm and calcific aortic valve stenosis. Studies have shown that two-dimensional transthoracic echocardiography yields little useful information in patients with arterial embolism. The advent of transesophageal echocardiography in the late 1980s allowed a more reliable identification of potential cardioembolic sources. The close contact of the echoprobe in the esophagus to the heart allows better resolution of intracardiac structures, particularly when cardiovascular abnormalities at the atrial level, the base of the heart and the thoracic aorta are sought. We studied 153 patients with clinically suspected arterial embolism by transthoracic and transesophageal echocardiography. Patients with extracranial carotide occlusive disease and patients older than 60 years were excluded from the study. In 88 out of 153 patients (58%) a cardioembolic mechanism could be detected by the combination of transthoracic and transesophageal echocardiography. Using the transthoracic method alone, a cardioembolic source could only be found in 55 patients (36%). Valvular heart disease and regional or global wall motion abnormalities could be visualized by both methods with similar results. However, only two out of 22 left atrial thrombi detected by transesophageal echocardiography could be documented also with the transthoracic approach. Transesophageal echocardiography was superior in the evaluation of valvular vegetations, intracardiac tumors, diseases of the thoracic aorta and abnormalities of the interatrial septum. Only left ventricular thrombi could be better evaluated by the transthoracic method, because visualization of the left ventricular apex by the transesophageal approach is problematic. In patients with systemic arterial embolism the combination of transthoracic and transesophageal echocardiography is the diagnostic method of choice to detect a cardioembolic source. Randomized studies in the future must prove, whether the echocardiographic findings can lead to better therapeutic strategies to improve the prognosis of patients with embolic disease.

Adult↗
PubMed1992

Domain flexibility in aspartic proteinases.

Comparison of the three-dimensional structures of native endothiapepsin (EC 3.4.23.6) and 15 endothiapepsin oligopeptide inhibitor complexes defined at high resolution by X-ray crystallography shows that endothiapepsin exists in two forms differing in the relative orientation of a domain comprising residues 190-302. There are relatively few interactions between the two parts of the enzyme; consequently, they can move as separate rigid bodies. A translational, librational, and screw analysis of the thermal parameters of endothiapepsin also supports a model in which the two parts can move relative to each other. In the comparison of different aspartic proteinases, the rms values are reduced by up to 47% when the two parts of the structure are superposed independently. This justifies description of the differences, including those between pepsinogen and pepsin (EC 3.4.34.1), as a rigid movement of one part relative to another although considerable distortions within the domains also occur. The consequence of the rigid body movement is a change in the shape of the active site cleft that is largest around the S3 pocket. This is associated with a different position and conformation of the inhibitors that are bound to the two endothiapepsin forms. The relevance of these observations to a model of the hydrolysis by aspartic proteinases is briefly discussed.

Aspartic Acid Endopeptidases↗
PubMed1992

The probable conformation of substrates recognized by dipeptidyl-peptidase IV and some aspects of the catalytic mechanism derived from theoretical investigations.

By theoretical conformational investigations of substrates and nonsubstrates of the enzyme dipeptidyl-peptidase IV (DP IV) as well as dipeptide-esters using the ECEPP83 method we determined the structure of peptides recognized and cleaved by the enzyme. From a comparison of all possible structures for the substrates with conformations not possible in nonsubstrates we concluded that a single conformation explains substrate specificities of DP IV. This conformation is characterized by the following dihedral angles: psi 1 = 85 degrees, omega 1 = 180 degrees, phi 2 = -75 degrees, psi 2 = 80 degrees, and omega 2 = 180 degrees. The conclusions were supported by comparisons of molecular electrostatic potentials calculated with the molecular graphics program HAMOG.

Amino Acid Sequence↗
PubMed1992

Diagnostic value of transesophageal echocardiography in atrial septal aneurysm.

Transthoracic and transesophageal echocardiography was performed in 40 consecutive adult patients with an atrial septal aneurysm. In 11 (27%) of 40 patients transthoracic echocardiography failed to demonstrate the lesion and the diagnosis was established by the transesophageal approach only. Interatrial shunting, assessed by echocardiographic contrast study and/or color flow mapping, was detected in 13 (54%) of 24 patients on transthoracic imaging and in 29 (76%) of 38 patients during transesophageal echocardiography. Identification of multiple fenestrations (n = 9) and thrombi within the aneurysm (n = 2) could be achieved only by transesophageal ultrasound. A cerebrovascular event of suspected embolic origin occurred in 20 (50%) of 40 patients; 11 (55%) of the 20 patients had repeated cerebral events. Except for mitral valve prolapse in 2 patients and spontaneous left atrial contrast phenomenon in 1 patient no other potential cardiac source of embolism could be identified by transesophageal echocardiography. A marked thickening of the aneurysm was present in 14 (70%) of 20 patients with a cerebrovascular event versus only 4 (20%) of 20 patients without a cerebrovascular event (p less than 0.01). The mechanism of embolization may be both primary thrombus formation within the aneurysm and paradoxical embolization through an interatrial communication as suggested by the findings on transesophageal ultrasound in 2 patients. Although the patients of this study represent a highly selected group it may be concluded that atrial septal aneurysm is a cardiac abnormality with embolic potential. Transesophageal echocardiography has to be regarded the imaging method of choice for evaluation of this lesion.

Adult↗
PubMed1992

[Step-plasty for therapy of chronic subcutaneous ruptures of extensor tendons of finger end joints].

A new method for secondary operative treatment of subcutaneous ruptures of the extensor tendons in the DIP-joint region is described. A step-cut incision is performed in the area of the regenerative tissue and the adjacent original tendon. The sutures in the longitudinal incision line compensate the tension and give better anchoring. First results show a tendency to an improved relationship between pre- and postoperative extension lag compared to other methods. Also, the method is an improvement from the aesthetical point of view and in operative practicability.

Adult↗
PubMed1992

[Sudden cardiac death: can individual risk be predicted?].

Only 30-40% of all victims of sudden cardiac death could so far be classified as risk patients during their lifetime. Risk factors for sudden death have little predictive value in an asymptomatic population: for example, the typical risk profile for the presence of coronary heart disease and changes in the surface-ECG at rest and especially in the surface-ECG under stress. Usually, the victims of sudden cardiac death among top performance athletes have been suffering from a heart disease of which they knew nothing beforehand: below 40 years of age, mostly from hypertrophic cardiomyopathy; beyond 40, predominantly from coronary heart disease. Among the heart diseases, sudden cardiac death is the cause of death most often in hypertrophic cardiomyopathy, in dilatative cardiomyopathy and in certain types of coronary heart disease. Notwithstanding the employment of fully update cardiological diagnostics the risk patients cannot be identified with reliable precision among those suffering from these diseases. It is only clinically manifest persistent ventricular tachycardia or successful reanimation in case of ventricular fibrillation that will definitely pinpoint the patient as being at risk of sudden cardiac death also in the future.

Cardiomyopathy, Dilated↗
PubMed1991

Mechanism and pathway of penicillopepsin-catalyzed transpeptidation and evidence for noncovalent trapping of amino acid and peptide intermediates.

Penicillopepsin acting on Nph-Ala2-amide (where Nph = p-nitrophenylalanyl) catalyzes a transpeptidation reaction which leads to the formation of Nph2-Ala2-amide, which arises from condensation of the substrate with enzyme-bound Nph, as the first product released from the enzyme. This is followed by a stage during which Nph3 and Ala2-amide are the major products. A small amount of Nph4 is also formed during this time. Nph and Nph2, formed during the reactions, are tightly, but probably not covalently, bound to the enzyme. They appear as free products only as a result of the cleavage of Nph3 and Nph4 and after most of the substrate Nph-Ala2-amide has been used up. They act as acceptors for the substrate and for Nph2-Ala2-amide. Nph3-Ala2-amide, formed by condensation of Nph-Ala2-amide or of Nph2-Ala2-amide with enzyme-bound Nph2 or Nph, respectively, is also released but is cleaved rapidly to give Nph3 and Ala2-amide. Incorporation of 18O from [18O]water into the carbonyl oxygens of the products is extensive and shows that release of the intermediates is slower than peptide bond cleavage and peptide bond formation. Hence the rate-limiting step in these reactions is product release. No 18O is incorporated into the initial substrate. We propose that Nph and Nph2 as intermediates are held in the active site by hydrogen bonds and by two strong electrostatic interactions.

Amino Acids↗