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Biomedical subjects

D Juretić

Publications and source records attributed to D Juretić.

14 recordsLinked to original sources
PubMed1992

Rapid and simple method for the determination of copper, manganese and zinc in rat liver by direct flame atomic absorption spectrometry.

An acidic homogenate method, which includes simple homogenization pre-treatment of tissue material and direct nebulization flame atomic absorption spectrometry (FAAS), is successfully applied to the simultaneous determination of copper, manganese and zinc in rat liver. The proposed method involves only a few steps for sample pre-treatment at room temperature, making the risk of systematic errors very small. Because recoveries of 101% for copper, 98% for manganese and 100% for zinc could be achieved using aqueous standards, matrix-matched standards were redundant. Favourable results obtained in biological media, including limits of detection of 0.04, 0.03 and 0.04 mg l-1 for Cu, Mn and Zn, respectively, together with accuracies of 0-3%, and relative standard deviations ranging from 2 to 10% are further evidence of the suitability of the method.

Animals↗
PubMed1991

Effect of ochratoxin A on brush border enzymes of rat kidney.

Ochratoxin A was given orally at 60 microgram/kg body weight in neutral olive oil to Fischer rats for 30 days, at which time they were killed. Clinical state, weights of animals and of their organs and urea and creatinine concentrations were not affected during the exposure period. Significant increases in the activity of enzymes in urine were found: 60% increase in alanine aminopeptidase, 45% increase in gamma-glutamyl-transferase and 90% increase in alkaline phosphatase. These changes indicate early pathological changes in the kidney. Relatively small amounts of the toxin thus affect kidney membrane cells.

Alkaline Phosphatase↗
PubMed1991

Application of the monodimensional electrophoresis for the separation of glycosaminoglycans on Cellogel cellulose acetate strip.

A monodimensional electrophoretic method for the separation of glycosaminoglycans on Titan III Zip Zone cellulose acetate plate based on their different electrophoretic mobilities in barium acetate and different solubilities in ethanol was applied to the Chemetron electrophoretic equipment. Improved timing of individual steps of electrophoretic run, additional cooling and pressure must be introduced for optimal separation of glycosaminoglycans mixture (dermatan sulphate, heparan sulphate, hyaluronic acid, chondroitin-4-sulphate, chondroitin-6-sulphate and keratan sulphate) resulting in five well separated sharp bands. By all these changes in the original procedure of Hopwood and Harrison, the separation of chondroitin-4-sulphate and chondroitin-6-sulphate was not achieved. The modified procedure on Cellogel strip is suitable for the screening of mucopolysaccharidoses.

Electrophoresis, Cellulose Acetate↗
PubMed1989

Interactions between a new class of eukaryotic antimicrobial agents and isolated rat liver mitochondria.

Members of a newly discovered class of eukaryotic antimicrobial peptides are shown to release respiratory control in isolated rat-liver mitochondria. They also dissipate the membrane potential and inhibit respiration. The uncoupling activity of the peptides decreases with time probably due to the presence of proteases in the mitochondrial preparation. Quinine and Mg2+ reduce the activity of the peptides. The nature of the dependence of the respiratory rate on the concentration of added peptides suggests that they are active in a multimeric form, consistent with the formation of a channel across the inner mitochondrial membrane. The channel allows passage of sucrose.

Animals↗
PubMed1989

Magainin 2 amide and analogues. Antimicrobial activity, membrane depolarization and susceptibility to proteolysis.

We compared the abilities of synthetic magainin 2 amide and its analogues to inhibit the growth of Escherichia coli and to cause membrane depolarization in E. coli cells and cytochrome oxidase liposomes. The analogue, magainin A, was about 40-times more active than magainin 2 amide in inhibiting the growth of E. coli and had a much more sustained effect on the membrane potential. In the liposomal system, however, there was only approx. 20% difference between these two peptides in the reduction of membrane potential and uncoupling of respiration. Studies with pronase digestion suggested that the difference in potency may be due to differential susceptibility to proteolysis in the presence of membranes.

Amides↗
PubMed1989

Magainins and the disruption of membrane-linked free-energy transduction.

Magainins, a family of positively charged peptides, are partly if not wholly responsible for antimicrobial activity in skin extracts of Xenopus laevis. We report here that members of the magainin family--i.e., the 21-amino acid peptide PGLa and the 23-amino acid peptide magainin 2 amide (PGSa)--dissipate the electric potential across various energy-transducing membranes and thus uncouple respiration from other free-energy-requiring processes. We propose that this is a likely mechanism for the antimicrobial effects of these compounds.

Animals↗
PubMed1987

Secondary structure predictions and medium range interactions.

Several authors have proposed that predictions of protein secondary structure derived from statistical information about the known structures can be improved when information about neighboring residues participating in short and medium range interactions is included. A substantial improvement shown here indicates that current methods of including this information are not more successful than methods that do not. Evaluations of the Chou and Fasman method (Adv. Enzymol. 47 (1978) 45-148), that does not include information about interactions (except in averaging), have shown it to be about 49% correct for three states (helix, beta-sheet and undefined). In comparison, the method of Garnier et al. (J. Mol. Biol. 120 (1978) 97-120), that explicitly includes information about neighboring residues, has an accuracy of 57% residues correct for three states. However, we have obtained an 8% improvement for predictions of secondary structure based on the algorithm by Chou and Fasman. The improvements are obtained by eliminating many rules and by choosing the best decision constants for structure assignments. The simplified method described here is 57% correct for three states using preference values calculated in 1978.

Amino Acids↗
PubMed1987

Variation of efficiency with free-energy dissipation in models of biological energy transduction.

For two models of biological free-energy transducers, it is investigated how free-energy dissipation and efficiency vary as (i) the demand for output free energy, (ii) the input free energy or (iii) the properties of the transducers themselves, are varied. One model is representative of near-equilibrium free-energy transducers in general, the other is a special case of far-from-equilibrium free-energy transduction, reminiscent of proton pumping by bacteriorhodopsin. It turns out that the relationship between efficiency and free-energy dissipation depends strongly on what varies. In some cases, free-energy dissipation increases as the efficiency increases. It is suggested that this is one reason why biological evolution has not resulted in high efficiencies and low rates of free-energy dissipation. For the near-equilibrium free-energy transducer, the free-energy dissipation at the static head steady state is minimal with respect to variations in the output force. For the far-from-equilibrium model (of bacteriorhodopsin), the static head does not correspond to such a minimum, if that free-energy transducer slips.

Bacteriorhodopsins↗
PubMed1986

Effects of neuroleptic phenothiazines on the activities of aminotransferases and gamma-glutamyltransferase in serum and liver.

Serum alanine aminotransferase, aspartate aminotransferase and gamma-glutamyltransferase activities were monitored in psychiatric patients receiving normal doses of phenothiazine neuroleptics over a 30-day period. The first two enzymes showed slight initial increases and a subsequent return to normal, while the third showed a slight increase. In rats, dosage levels exceeding those used in human therapy produced much larger increases in the catalytic concentrations of all three enzymes in serum (1.4, 0.7 and 0.5 above the control value, respectively), and somewhat smaller increases in the liver homogenates of these animals.

Animals↗
PubMed1977

The effect of phosphatidylcholine depletion on biochemical and physical properties of a Neurospora crassa membrane mutant.

By using the choline starvation process it is possible to deplete the membranes of Neurospora crassa choline auxotroph chol-1 of phosphatidylcholine, without affecting the viability of germinated spores or whole mycelium. Spin label probes were used to examine the possible dependence of the physical state of cellular lipids on the presence of phosphatidylcholine in the membranes. Increased freedom of rotational motion of lipid soluble probes was regularly detected in choline-starved mycelium. The accumulation of neutral lipids (mostly triglycerides) in bulk form was also observed during the choline starvation process. The experiments with isolated and separated lipid classes indicated that the observed increase in fluidity of lipids in choline-starved mycelium is partly due to the difference in physical properties between bulk lipids and membrane lipids. Spin label probe 2N4 (2-propyl-2,5,5-trimethyloxazolidine-N-oxyl), which can partition at the membrane-water interface, exhibited easier partitioning among membrane lipids of choline-starved mycelium.

Cell Membrane↗
PubMedDate not supplied

Tryptophan content in serum and brain of long-term insulin-treated diabetic rats.

The metabolism of tryptophan (TRP) was studied in diabetic and insulin-treated diabetic rats throughout a five-month period. In alloxan diabetic rats the serum and brain TRP levels were decreased (serum: 38 to 48 mmol/l, brain: 8.6 to 9.2 mmol/g) in comparison to the values of control rats (serum: 59 to 64 mmol/l, brain: 11.3 to 12.6 mmol/g). Daily long-term (for 45, 75, 90 or 135 days) treatment with intermediately acting insulin (4 IU/rat, s.c.) was not able to restore brain concentration of TRP. On the contrary, the serum TRP concentrations were totally or partially restored. The concentrations of branched chain amino acids (BCAA) were increased in serum (valine = 361.2 to 461.0 mumol/l or leucine + isoleucine = 431.0 to 520.3 mumol/l) throughout the entire five-month examination period. Insulin treatment did not return serum concentration of BCAA to normal level in the observation period either.

Amino Acids↗