Biomedical subjects

P Racay

Publications and source records attributed to P Racay.

21 records · Page 2Linked to original sources

PubMed1994

Alteration in rabbit brain endoplasmic reticulum Ca2+ transport by free oxygen radicals in vitro.

The involvement of free oxygen radicals in ischemia-reperfusion injury is generally accepted. We describe here the loss of efficiency of reticular membranes to sequester Ca2+ due to free oxygen radical damage in vitro. Based on experimental results we suggest that the primary effect of free oxygen radicals is alteration of the lipid component of the membrane manifested in the increase of passive Ca2+ leak. Prolonged treatment of microsomes with free oxygen radical generating systems also led to the decrease of Ca(2+)-ATPase activity which is caused as we suppose by modulation of the lipid-Ca2+ pump interactions. A protective effect of butylated hydroxytoluene on the depression in the Ca2+ uptake and Ca(2+)-ATPase activities supports our suggestions.

Animals↗

PubMed1994

Intracellular Ca2+ store from rabbit brain: kinetic aspects of Ca(2+)-stimulated ATPase.

The endoplasmic reticulum of the rabbit brain manifests low but distinguishable Ca(2+)-stimulated ATPase activity with some functional peculiarities compared to the muscle isoforms. The activity is highly sensitive to the presence of detergents and optimal activatory concentration was shown to be close to the critical micellar concentration. Kinetic properties, such as (i) activation by low (K0.5 = 0.45 microM) and inhibition by high (more than 100 microM) concentration of calcium, (ii) biphasic activation with ATP and (iii) inhibition by vanadate clearly showed that the protein of Ca(2+)-ATPase is endowed with properties typical of the family of sarco/endoplasmic reticulum calcium pumps.

Adenosine Triphosphate↗

PubMed1992

Characteristics of NADPH-dependent thymidylate synthetase purified from Streptomyces aureofaciens.

NADPH-dependent thymidylate synthetase from Streptomyces aureofaciens has been purified to homogenity by a two-step chromatographic procedure including anion-exchange chromatography and affinity chromatography on methotrexate-Sepharose 4B. The enzyme was purified 1025-fold with a 34% yield. Basic characteristics of the enzyme were determined: molecular weight of the enzyme subunit (28,000), pH and temperature optimum, effect of cations, dependency on reducing agents, Km values for dUMP, mTHF, and NADPH (3.78, 21.1, and 38.9 microM, respectively), and inhibition effect of 5-FdUMP. Binding studies revealed the enzyme mechanism to be ordered sequential: dUMP bound before mTHF. S. aureofaciens thymidylate synthetase exhibits an absolute requirement for NADPH for the enzyme activity--a unique feature not displayed by any of the thymidylate synthetases isolated so far. NADPH is not consumed during enzyme reaction, indicating its regulatory role. The properties of S. aureofaciens thymidylate synthetase show that it is a monofunctional bacterial enzyme.

Chromatography, Affinity↗