[A multimedia atlas of skin pathology]. / Multimediální atlas kozní patologie.

We prepared a digital atlas of non-tumourous skin pathology. Currently, the available digital atlases can go beyond the scope of written publications, especially with regards to ease of access, speed of preparation, updating information, fair price and unlimited capacity. This atlas can be used as a diagnostic aid, as well as for postgraduate and pregraduate teaching.

MAPOS: a computer program for organic synthesis design based on synthon model of organic chemistry.

The program MAPOS is a logically oriented computer program for computer-aided organic synthesis design suitable both for forward and retrosynthetic synthesis planning. It is based on the synthon model of organic chemistry, introduced by the authors. The fundamentals of the model as well as the basic algorithms are described. Examples of the use of the program are given.

Binding of ligands to horse liver alcohol dehydrogenase lacking zinc ions at the active sites.

The zinc-deficient enzyme binds the fluorescence probes for the enzyme substrate pocket (auramine O, 13-ethylberberine, chlorprothixene and acridine orange) more tightly than the native enzyme, whereas 1-anilinonaphthalene 8-sulphonic acid is bound with comparable affinity. The use of fluorescence probes as reporter ligands revealed that the formation of binary complexes between the zinc-deficient enzyme and aldehydes is possible (as with the native enzyme) and confirmed an increased affinity of coenzymes to the modified enzyme. The absence of catalytic zinc ions brings about a loss of the essential stabilization effect in simultaneous NADH and aldehyde binding to liver alcohol dehydrogenase. 2,2'-Bipyridine, which chelates the active-site zinc ion in the native enzyme, is bound rather loosely to the same site as aldehydes, auramine O and ethylberberine in the case of the zinc-depleted enzyme. The stopped-flow measurements showed that the pH dependence of auramine O and ethylberberine binding to native and zinc-depleted enzyme is essentially similar. These data are compatible with the presence of ionizable groups in the surroundings of the bound probes. This group might be either His-67, bound to the zinc ion, or the zinc-liganding water molecule in the case of the native enzyme (pK close to 9), or the free His-67 residue in the case of the zinc-deficient enzyme (pK about 8).

Comparison of several non-linear-regression methods for fitting the Michaelis-Menten equation.

The known jackknife methods (i.e. standard jackknife, weighted jackknife, linear jackknife and weighted linear jackknife) for the determination of the parameters (as well as of their confidence regions) were tested and compared with the simple Marquardt's technique (comprising the calculation of confidence intervals from the variance-co-variance matrix). The simulated data corresponding to the Michaelis-Menten equation with defined structure and magnitude of error of the dependent variable were used for fitting. There were no essential differences between the results of both point and interval parameter estimations by the tested methods. Marquardt's procedure yielded slightly better results than the jackknives for five scattered data points (the use of this method is advisable for routine analyses). The classical jackknife was slightly superior to the other methods for 20 data points (this method can be recommended for very precise calculations if great numbers of data are available). The weighting does not seem to be necessary in this type of equation because the parameter estimates obtained with all methods with the use of constant weights were comparable with those calculated with the weights corresponding exactly to the real error structure whereas the relative weighting led to rather worse results.

Interaction of yeast alcohol dehydrogenase with protoberberine alkaloids.

Oxidation of ethanol and reduction of aldehyde catalysed by yeast alcohol dehydrogenase is inhibited by several naturally occurring as well as semi-synthetic protoberberine alkaloids. The affinity of these compounds for the enzyme depends essentially on their hydrophobicity. Corysamine and coptisine are the most potent inhibitors among the natural alkaloids of this group. The kinetics of yeast alcohol dehydrogenase inhibition with coptisine were analysed and equilibrium measurements using optical methods were carried out. The results suggest that the binding site of the enzyme for protoberberines is not identical with those for coenzyme and substrate though it should be located near the nicotinamide ring of bound NAD. The binding of protoberberines seems to be limited to rather superficially located hydrophobic groups in the vicinity of the active site of the enzyme. The inability of these alkaloids to protrude deeply into the molecule of yeast alcohol dehydrogenase at the catalytically important region is the main difference in their behaviour towards alcohol dehydrogenases from yeast and horse liver.

Steady-state kinetics of horse-liver alcohol dehydrogenase with a covalently bound coenzyme analogue.

The steady-state kinetics of the enzyme modified by affinity labelling with NAD analogue, nicotinamide-N6-[N-(6-aminohexyl)carbamoylmethyl]-adenine dinucleotide, has been investigated using a recycling reaction with p-nitrosodimethylaniline and n-butanol as substrates and compared to the kinetics of native alcohol dehydrogenase. The modified enzyme obeys a ping-pong mechanism involving two inactive enzyme forms (enzyme-NAD and enzyme-NADH complexes in the 'open' conformations, the nicotinamide moieties of the coenzymes being out of the active center). The rate of p-nitrosodimethylaniline reduction in the reaction catalyzed by the modified enzyme is comparable to that observed in the presence of the native enzyme. On the other hand, the oxidation of butanol by the modified enzyme is essentially slower under our experimental conditions (pH 8.5). The measurements in the presence of specific alcohol dehydrogenase inhibitors competing with substrates and coenzymes (isobutyramide, pyrazole and AMP) revealed that the relative portion of the inactive 'open' form of the enzyme-NADH complex is negligible, whereas the 'open' form of the enzyme-NAD complex seems to represent a more significant portion (about 30%) under the conditions used.