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Biomedical subjects

K Buchholz

Publications and source records attributed to K Buchholz.

42 records · Page 3Linked to original sources
PubMed1976

Temperature dependence of a diffusion-limited immobilized enzyme reaction.

The apparent activation energy of N-alpha-benzoyl-L-arginine-ethyl ester (BAEE) hydrolysis by immobilized trypsin varies with the bulk substrate concentration from its maximum value, comparable to that of the free enzyme, to considerably lower values. Thus, with a concentration change from 3 x 10(-2) to 10(-4) M the apparent activation energy diminishes from 9.5 to 4.5 kcal/mol. This experimental finding is interpreted to be due to Michaelis-type kinetics in a heterogeneous system, in one case reflecting the temperature dependence of the maximal enzyme reaction rate, in another case illustrating the diffusion limited overall reaction at low substrate concentrations. As a consequence it may not be feasible to operate a reaction at elevated temperatures in a high conversion range, since diffusion limitation may restrict the enhancement of the overall reaction rate. Some further data are given concerning the buffer effect on the reaction rate, which should occur due to its limitation by proton transfer in the buffer-free system.

Arginine↗
PubMed1975

[Unusual clinical forms of pseudo-LE syndrome: an induced immune-complex disease? (author's transl)].

Two of nine patients with pseudo-LE syndrome had previously undescribed organ manifestations. In one there was the full-blown picture of cutaneous lupus erythematodes, with renal and CNS involvement, ending fatally. Immunohistologically there was severe vasculitis and nephritis, histologically generalised necrotizing angitis. It is possible that the dramatic clinical picture was due to alpha-methyldopa. In the second case lymphadenopathy with bihilar involvement and splenomegaly predominated. Histologically there was no evidence of Boeck's sarcoid. Further studies revealed systemic involvement with immune-complex nephritis, electron-dense deposits in the glomerular basal membrane, and the typical changes of lupus erythematodes in the marrow. In a third case there were similar changes in kidney and marrow. These findings support the view of an immune-complex disease which can be fatal. An unusual feature in seven of the nine patients was the proven intake of Venopyronum¿ coated tablets in temporal relationship to the manifestation of the disease. It is possible that the described cases of pseudo-LE syndrome were drug-induced. The immunological mechanism of the disease would, in that case, be analogous to penicillamine nephropathy.

Adult↗
PubMedDate not supplied

The effect of pH and oxygen concentration on the formation of 3-ketodisaccharides by Agrobacterium tumefaciens.

The further optimization of 3-ketodisaccharide formation with sucrose, leucrose and iso maltulose was studied with special regard to pH and oxygen concentration in the reaction mixture with resting cells of Agrobacterium tumefaciens. It was found that the optimal pH values for the highest reaction rate and highest yield were different as the pH affected the stability of the 3-keto derivatives formed. A pH shift to 5.0 clearly reduced the enzymatic degradation of the 3-keto derivatives thus stabilizing them. The influence of constant oxygen concentrations on 3-ketosucrose formation was tested showing results not explicable with normal Michaelis-Menten kinetics. For each substrate a maximum of reaction rate and yield were obtained at very low oxygen concentrations.

Agrobacterium tumefaciens↗
PubMedDate not supplied

Anaerobic degradation of poly-3-hydroxybutyrate and poly-3-hydroxybutyrate-co-3-hydroxyvalerate.

The anaerobic degradation of the polyesters poly-3-hydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) was investigated with special regard to intermediate products, kinetics, and yields. During the degradation of PHBV acetate, propionate, n-butyrate, and n-valerate were detected. Additionally, 3-hydroxybutyrate and 3-hydroxyvalerate and four dimeric esters of these two molecules were identified by GC-MS measurements. Three different test systems for the anaerobic degradation of polyesters were studied. It was not possible to get reproducible results by means of the Anaerobic Sturm-test, a simple system based on carbon dioxide measurement. Secondly, a system based on the GC measurement of accumulated organic acids was investigated. A degradation of 90% in two days was calculated by a carbon balance. Best results were reached with the third test system based on the measurement of methane with a gas meter. A degradation of 99% was observed within 30 days.

Anaerobiosis↗