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Biomedical subjects

A Fricker

Publications and source records attributed to A Fricker.

At least 19 recordsLinked to original sources
PubMed1994

Intramolecular recombination in polyomavirus DNA is a nonconservative process directed from the viral intergenic region.

Previously, we have studied intramolecular homologous recombination in polyomavirus replicons under conditions allowing only one amplifiable recombination product to be generated from a single precursor molecule. In order to detect putative reciprocal product(s), we have now constructed precursor polyomavirus replicons which contain two copies, instead of one copy, of the viral intergenic region, including the origin of replication as well as both promoters. Upon transfection of mouse cells, constructs containing directly repeated intergenic regions yielded distinct amplifiable products, in number depending upon the functional integrity of both intergenic regions. Our data indicate that of two possible reciprocal products, a given precursor molecule would yield either one or the other but never both at the same time. Most striking, however, is the observation that promoter function is required for recombination, while the origin of replication function may be needed only for amplification of the recombination product once it has been formed. The data reported here confirm and extend previous data suggesting that (i) transcription is instrumental in recombination between direct repeats and (ii) nonconservative recombination involving direct repeats relies upon two promoters of opposing polarities.

DNA, Viral↗
PubMed1981

Enzymatic degradation of polar lipids in deep-frozen parsley.

Under the frozen storage at usual storage temperatures of leafy tissues not pretreated by heat, enzymatic lipid degradation reactions take place, which lead already after a few weeks to a considerable or complete loss of the native polar lipids. These degradation processes being accompanied by a deterioration of the flavour have been studied in greater detail in parsley leaves. Among the reaction products we found large amounts of 6-acylmonogalactosyl diglycerides (formed from monogalactosyl diglycerides by enzymatic transacylation) and phosphatidic acid (formed from phospholipids through phospholipase-D action). The generally assumed reaction sequence: formation of free fatty acids by acyl hydrolases followed by hydroperoxidation through lipoxygenase and degradation of the hydroperoxidation through lipoxygenase and degradation of the hydroperoxides into off-flavour compounds may hence take place, if at all, only to a limited extent. Considerable phospholipase D as well as minor acyl transferase activities are detected at --24 degrees C, whereas at --32 degrees C the lipid loss is very low. Deterioration processes can be avoided by blanching, a treatment not leading to any substantial quality loss.

Food Handling↗
PubMed1977

[The reaction of holo-, apo- and coenzyme of the peroxidase to heating (author's transl)].

The thermal reaction of the two components of the horseradish peroxidase--the apoenzyme and the prosthetic group--with that of the holoenzyme were compared. From this we conclude that the thermal inactivation of the peroxidase in aqueous solution is not caused by a change of the apoprotein alone, but rather by participation of the entire three-dimensional structure including the prosthetic group. Spectrophotometric studies of the inactivation process in the holoenzyme revealed that the absorbance of the Soret band changes parallely to a reduction of the enzyme activity during heating. Since it has been found that the Soret absorption increases again during storage and simultaneously the enzyme activity regenerates, the change of the Soret absorption during heating can be regarded as the result of both reversible and irreversible denaturation processes.

Apoenzymes↗
PubMed1977

[Thermal inactivation and storage behavior of technologically important enzymes. I. Horseradish and spinach peroxidase].

The thermal inactivation and storage behaviour for horseradish and spinach peroxidases were investigated in defined systems, in spinach also within its natural environment. The inactivation curves of either enzyme show a sharp bend which is clearly visible at low, but not at higher temperatures. The D-values were taken from the inactivation curves. z-values resulting from the D-values were 25.5 degrees C for horseradish peroxidase, 13 degrees C for isolated peroxidase and 18 degrees C for peroxidase in spinach extract. Horseradish peroxidase was relatively heat-resistent at pH 6.0, spinach peroxidase at pH 5.0-6.0; both enzymes were found to be highly susceptible to heat at pH 4.0. Peroxidase isolated from spinach responded differently to heating than the enzyme in spinach extract or suspension. This discrepancy indicates that certain model experiments cannot be transferred to foods. Heated peroxidase from horseradish and spinach were found to regenerate during storage; the extent of regeneration depended on the pH.

Drug Stability↗
PubMed1977

[Thermal inactivation and storage behavior of technologically important enzymes. II. Lipase from Geotrichum candidum and lipoxygenase from soybeans].

The thermal inactivation of lipase out of Geotrichum candidum and of lipoxigenase out of soybeans was investigated in phosphate buffer solution. Comparable to peroxidase, a sharp bend was observed in the inactivation curves of both enzymes. The z-value of 19 degrees C for lipase out of Geotrichum candidum was higher than the values indicated in the pertinent literature for pancreas lipase and milk lipase. The z-value for soy lipoxigenase was found to be 9.8 degrees C.

Drug Stability↗
PubMed1977

[Thermal inactivation and storage behavior of technologically important enzymes. III. Effect of reagents added to peroxidase and lipoxygenase].

The influence of milieu factors on the thermal inactivation of peroxidase and lipoxigenase was investigated. Cationogenic, anionogenic, non-ionogenic and amphoteric tensides were more or less effective in inactivating horseradish peroxidase. Most effective in this respect were lecithine and monoglyceride, both capable of swelling in water. In presence of lecithine, peroxidase was inactivated already at 0 degrees C and pH 4.0. Linoleic acid was more efficient in an oxygen stream than in presence of nitrogen, in a stream of nitrogen its influence was comparable to oleic acid. This suggests an additional effect by lipid peroxides which are formed of linoleic acid under the heating process. Tensides prevented the regeneration of the heated peroxidase. In the case of lipoxigenase, the authors investigated the influence of lecithine and various fatty acids on the thermal inactivation at 60 degrees and pH 7.0. Lecithine accelerated the inactivation less distinctly than with peroxidase. The accelerated the inactivation less distinctly than with peroxidase. The accelerating effect of the fatty acids decreased in the order oleic acid, linoleic acid, palmitic acid, myristic acid and stearic acid.

Drug Stability↗
PubMed1977

[Thermal inactivation and storage behavior of technologically important enzymes. IV. Spinach lipid-acyl-hydrolase].

The thermal reaction of a lipid-acyl-hydrolase which seems to be important for the quality preservation of vegetable foods, was investigated in spinach. The authors applied a simple in-situ method using thin-layer chromatography which had been developed for the enzyme determination, to follow the thermal inactivation of the lipid-acyl-hydrolase by measuring the decomposition of lecithin, mono- und digalactosyl diglycerides. According to the inactivation curves, the enzyme is relatively little resistant to heat. Since the D- and z-values resulting from the inactivation curves for phospholipase, mono- and digalacto-lipase activities are almost the same, it can be assumed that the lipid-acyl-hydrolase is a multi-function enzyme in spinach.

Drug Stability↗
PubMed1975

Child abuse.

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Child↗