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T Bellini

Publications and source records attributed to T Bellini.

53 records · Page 3Linked to original sources
PubMed1989

Effect of 17 beta-estradiol on partition behavior of human erythrocytes in dextran-poly(ethylene glycol) aqueous phases.

Preincubation with 1 nM 17 beta-estradiol changes the partition behaviour of human erythrocytes in dextran-poly(ethylene glycol) aqueous phases. Erythrocyte partition decreases reaching a minimum after 5 min of incubation, then slowly increases returning to starting values after 30 min. The effect is specifically induced by the isomer of estradiol, whereas the alpha isomer and other steroid hormones (progesterone, testosterone and 5 alpha-dihydrotestosterone) are uneffective. The effect of the hormone can be suppressed by treatment of erythrocytes with either N-ethyl maleimide, sodium vanadate, or ouabain, or carrying out incubations in potassium-free buffer. These data suggest that the effect of estradiol on phase partition of erythrocytes is mediated by the (Na,K)-ATPase.

Dextrans↗
PubMed1986

Myelin basic protein inhibits formyl-peptide induced chemotaxis in human neutrophils.

Myelin basic protein, one of the major membrane protein component of the central nervous system, was used to probe the molecular mechanism of cellular activation. Pre-treatment of human neutrophils with myelin basic protein selectively inhibits the formyl-peptide-induced chemotaxis, without affecting chemotaxis evoked by casein and activated serum. Furthermore, both the degranulation and superoxide anion production stimulated by the chemotactic peptide are not modified by the prior treatment of the neutrophils with myelin basic protein.

Calcium↗
PubMed1986

A rapid method for purification of myelin basic protein.

A rapid procedure for purification of myelin basic protein has been developed. White matter is delipidated with 2-butanol, and the residue is extracted at pH 7.5 and 8.5. Myelin basic protein is solubilized by extraction in acetate buffer, pH 4.5. The entire procedure requires less than 4 h, and gives homogeneous protein essentially free of protease activity. This procedure can be scaled down to process milligram amounts of white matter; thus it can be very useful for purification of myelin basic protein from very limited amounts of human white matter obtained during surgery.

Acetates↗
PubMed1985

Half-site reactivity in 6-phosphogluconate dehydrogenase from human erythrocytes.

6-Phosphogluconate dehydrogenase from human erythrocytes was purified by an improved procedure. Binding studies showed that the dimeric enzyme binds 2 mol of NADP+/mol but only 1 mol of NADPH/mol, and that the bindings of oxidized and reduced coenzyme are mutually exclusive. From initial-rate kinetics and inhibition studies, a sequential random-order mechanism is proposed. Double-reciprocal plots with NADP+ as varied substrate show a downward curvature, indicating a negative co-operativity. We suggest that the negative co-operativity observed kinetically is a result of the half-site reactivity for the NADPH. The different binding stoichiometries for NADP+ and NADPH generate a non-linear relationship between the apparent dissociation constant for the NADPH and the concentrations of the NADP+, resulting in a regulatory mechanism highly sensitive to the changes in the NADP+/NADPH ratio.

Binding Sites↗
PubMed1985

The NADP binding site on rabbit muscle aldolase.

Rabbit muscle aldolase binds NADPH with a 1:1 stoichiometry and with a dissociation constant 18 microM. Three sites of the dinucleotide are involved in the binding: the adenosyl diphosphate moiety, the nicotinamide-ribose, and the nicotinamide ring. These data show the existence of a specific dinucleotide binding site in the aldolase molecule.

Animals↗
PubMed1982

Non-enzymic protein phosphorylation. Phosphorylation of 6-phosphogluconate dehydrogenase by acyl phosphates.

Incubation of 6-phosphogluconate dehydrogenase from Candida utilis with either acetyl phosphate, 1,3-diphosphoglycerate or carbamoyl phosphate results in the phosphorylation of the protein. The binding of one phosphate residue per enzyme subunit does not affect significantly the kinetic properties, but makes the enzyme less reactive toward thiol reagents, trypsin and pyridoxal 5'-phosphate. We suggest indicate that: (1) 6-phosphogluconate dehydrogenase from C. utilis is phosphorylated non-enzymically by physiological acyl phosphates and (2) the phosphorylation of the enzyme modifies the rate of protein inactivation.

Amino Acids↗
PubMed1981

Substrate-induced intramolecular proton transfer in 6-phosphogluconate dehydrogenase from Candida utilis.

Formation of binary complex between 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate:NADP+ 2-oxidoreductase (decarboxylating), EC 1.1.1.44) from Candida utilis and 6-phosphogluconate was investigated by means of ultraviolet difference spectroscopy. The formation of the enzyme-substrate complex induces in the difference spectrum a positive peak the wavelength and extinction coefficient of which agree well with a tyrosine ionization. Titrimetric studies indicate that the formation of the binary complex is not coupled to a proton release from the protein. These data support an intramolecular proton transfer from a tyrosine to other functional group. This proton transfer could be correlated to the conformational change induced by substrate in 6-phosphogluconate dehydrogenase.

Candida↗
PubMed1981

Effect of the substrate on the binding of coenzyme and coenzyme analogues to 6-phosphogluconate dehydrogenase from Candida utilis.

6-Phosphogluconate dehydrogenase from Candida utilis is a dimeric enzyme with apparently identical subunits. Two coenzyme analogues, periodate-oxidized NADP+ and 3-amino pyridine adenine dinucleotide phosphate, bind to the protein with Kdiss of 42 microM and 6.2 microM, respectively. NADPH binds to the enzyme with a Kdiss of 0.42 microM. Both coenzyme and coenzyme analogues show "all-of-the sites reactivity." In the presence of the substrate 6-phosphogluconate, the Kdiss of the coenzyme analogues is lowered to 3.5 microM and 2.4 microM, respectively, whereas the Kdiss of NADPH is increased to 2.7 microM. Coenzyme analogues, but not NADPH, show an half of-the sites reactivity in the presence of 6-phosphogluconate. The enzymatic activity is inhibited by high NADP+ concentrations in presence of low concentrations of substrate, whereas at high substrate concentrations no inhibition by NADP+ is showed. These data suggest that: 1) the enzyme exhibits an half-of-the-sites reactivity during the catalytic cycle; 2) the recycle of the enzyme occurs mainly through an abortive ternary complex enzyme-substrate-NADPH.

Candida↗
PubMed1981

[[[Purification and properties of 6-phosphogluconate dehydrogenase from human erythrocytes].

6-phosphogluconate dehydrogenase was purified from human erythrocytes by chromatography on 2'5' ADP Sepharose and ammonium sulfate precipitation, to a specific activity of 28 IU/mg of protein. The enzyme binds two NADP molecules per molecule of dimer with a Kd of 6.95 microM, or only one molecule of NADPH per molecule of dimer with a Kd of 0.38 microM. The substrate has no effect on the binding of NADPH, whereas increases the binding of a coenzyme analogue, the NADP oxidized with periodate. These findings indicate a possible regulatory role for 6-phosphogluconate dehydrogenase.

Chromatography, Affinity↗
PubMed1981

The effect of inorganic phosphate on the stability of some enzymes.

In the presence of 5nM-P1, 6-phosphogluconate dehydrogenase from the yeast Candida utilis is more resistant to proteolysis and to the inactivating action of some chemical and physical agents. P1 also protects other enzymes against proteolysis. A hypothesis for the mechanism of the stabilizing action of P1 is advanced.

Candida↗
PubMed1981

Evidence for multiple pairs of vicinal thiols in some proteins.

The oxidizing agent periodate has been used as an analogue of phosphate. The reaction of periodate with some enzymes which have a phosphate-binding site causes only the formation of disulfide bridges and the loss of the catalytic activity. Phosphate and other tetrahedral anions protect against inactivation. Other enzymes are not inactivated by periodate, which seems to be specific for vicinal thiols. The results obtained suggest (a) the use of periodate for the detection of vicinal thiols in proteins, (b) the presence of multiple pairs of vicinal thiols in the proteins tested, and (c) the presence of these pairs at a phosphate-binding site. An hypothesis on the chemical structure of the phosphate-binding site of some proteins is advanced.

Alcohol Oxidoreductases↗
PubMed1979

Affinity labelling of the NADP+-binding site of glucose 6-phosphate dehydrogenase from Candida utilis.

1. Periodate-oxidized NADP+ inhibits the catalytic activity of glucose 6-phosphate dehydrogenase from Candida utilis, competing with NADP+. 2. Incubation of the enzyme with the coenzyme analogue causes partial reversible inactivation of the enzyme as a result of affinity labelling of the coenzyme-binding site. 3. Some kinetic values of the reaction were calculated. 4. The inactivation can be made irreversible by treatment with NaBH4, which reduces a Schiff base formed between an aldehyde group on the coenzyme analogue and a lysine residue on the enzyme. 5. Complete inactivation can be correlated with the binding of only one inhibitor to each enzyme subunit. 6. The lysine residue involved in the binding of the inhibitor is present at the coenzyme-binding site.

Affinity Labels↗
PubMedDate not supplied

Evidence for the proximity of a cysteine and a lysine residue in the active site of 6-phosphogluconate dehydrogenase from Candida utilis.

The environment of a cysteine residue in the active site of 6-phosphogluconate dehydrogenase from Candida utilis was investigated by means of N-(3-pyrene) maleimide. The reaction between enzyme and inhibitor results in the modification of one cysteine residue per enzyme subunit, and in the complete inactivation of the enzyme. In a second step, the epsilon-amino group of a lysine residue causes an intramolecular aminolysis of the bound inhibitor. These results indicate that a lysine and a cysteine residues are close in the three-dimensional structure of the active site of 6-phosphogluconate dehydrogenase.

Amino Acid Sequence↗