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Biomedical subjects

E Hubert

Publications and source records attributed to E Hubert.

At least 37 records · Page 2Linked to original sources
PubMed1986

Potassium activation and its relationship to a highly reactive cysteine residue in fructose 1,6-bisphosphatase.

The specific chemical modification by sodium cyanate of highly reactive cysteine residues at pH 7.5 in pig kidney fructose 1,6-bisphosphatase results in the reversible loss of activation of the enzyme by monovalent cations. No loss of activation by potassium ions occurs when modification is carried out in the presence of fructose 2,6-bisphosphate. The effect of Mg2+ on native and cyanate-modified enzyme activities implicates the above cysteine residue as being directly linked to the inhibition by both the divalent cation and fructose 2,6-bisphosphate. Incorporation of [14C]cyanate to the enzyme shows that the blockage of two reactive residues per tetramer is sufficient to eliminate the activation of the enzyme by K+.

Chromatography↗
PubMed1985

The reactive cysteine residue of pig kidney fructose 1,6-bisphosphatase is related to a fructose 2,6-bisphosphate allosteric site.

Modification of a highly reactive cysteine residue of pig kidney fructose 1,6-bisphosphatase with N-ethylmaleimide results in the loss of activation of the enzyme by monovalent cations. Low concentrations of fructose 2,6-bisphosphate or high (inhibitory) levels of fructose 1,6-bisphosphate protect the enzyme against the loss of monovalent cation activation, while non-inhibitory concentrations of the substrate gave partial protection. The allosteric inhibitor AMP markedly increases the reactivity of the cysteine residue. The results indicate that fructose 2,6-bisphosphate can protect the enzyme against the loss of potassium activation by binding to an allosteric site. High levels of fructose 1,6-bisphosphate probably inhibit the enzyme by binding to this allosteric site.

Animals↗
PubMed1985

Activation of fructose-1,6-bisphosphatases by monovalent cations and its relationship with a fructose-2,6-bisphosphate allosteric site.

The effects of potassium ions on pig kidney fructose-1,6-bisphosphatase activity have been studied. At low (non-inhibitory) concentrations of fructose-1,6-bisphosphate K+ shows an inhibitory effect and the apparent Km for fructose-1,6-bisphosphate increases as the concentration of monovalent cation increases. The inhibition by high substrate concentrations is decreased by addition of the potassium ions. Modification of a highly reactive cysteine residue with cyanate or N-ethylmaleimide results in the loss of activation of the enzyme by K+. Significant protection to the loss of potassium activation and substrate inhibition is afforded by the presence of low concentrations of fructose-2,6-bisphosphate or inhibitory levels of fructose-1,6-bisphosphate. Non-inhibitory concentrations of the substrate give partial protection against the loss of monovalent cation activation. The inhibitor AMP markedly increases the reactivity of the cysteine residue. The carbamoylated enzyme is not inhibited by excess of Mg2+ as compared to native enzyme. The results suggest that K+ decreases the affinity of the enzyme for fructose-1,6-bisphosphate at both the catalytic site and an allosteric site for fructose-2,6-bisphosphate. Furthermore, they lead to the proposal that monovalent cations activation could be due to the removal of both Mg2+ and substrate inhibitions.

Animals↗
PubMed1984

Selective tryptic cleavage of native cytoplasmic aspartate transaminase holoenzyme.

The cytoplasmic isozyme of aspartate transaminase is inactivated by trypsin due to loss of a 19-residue peptide from the NH2-terminal region. A second peptide bond at Arg-25 is then cleaved by trypsin leaving a residual core protein, transaminase 26-412. Inactivation by trypsin resembles that for the mitochondrial enzyme (Sandmeier, E., and Christen, P. (1980) J. Biol. Chem. 255, 10284-10289), yet occurs 10 times faster for the cytoplasmic isozyme. In the mitochondrial enzyme, trypsin cleavage produces equal concentrations of proteins missing the first 26 and 31 amino acids. Sequence variation in the NH2-terminal regions can explain such differences. Specifically, the mitochondrial NH2 terminus has no trypsin-susceptible residue at position 19 and is stabilized by an electrostatic interaction between Asp-15 and Arg-292, whereas position 15 is a valyl residue in the cytoplasmic enzyme. Calorimetric data reveal both a decreased transition temperature (Td) and enthalpy (delta Hd) of denaturation in transaminases 20-412 and 26-412. Interaction of substrates with the active site chromophore and differential scanning calorimetry (DSC) reveal that catalytically inactive transaminases 20-412 and 26-412 can bind amino acid substrates and produce spectroscopically detectable conversion of the pyridoxal to the pyridoxamine form of the protein. By contrast, substrate analogs only form enzymatic Michaelis-type complexes.

Amino Acid Sequence↗
PubMed1982

Study of helper and suppressor T-cells in cystic fibrosis.

The ratio between inducer and cytotoxic/suppressor subset T-cells was studied in 11 cystic fibrosis patients and 11 non-cystic fibrosis controls. No statistically significant difference was found between the two groups. It is suggested that the major immune deficiency in some patients suffering from cystic fibrosis is a state of tolerance to the same bacterial antigens such as Pseudomonas aeruginosa. Inhibitory factors are present in the serum of the most affected patients.

Adolescent↗
PubMed1979

Localization of oxidized nocotinamide--adenine dinucleotide glycohydrolase in the mouse liver nuclear envelope.

NAD+ glycohydrolase activity located in the nuclear envelope was maximally solubilized by treatment with 0.1--0.2% Triton X-100. The residual activity largely represents the chromatin-associated NAD+ glycohydrolase. Under these conditions the phospholipids were extensively solubilized (over 90%) while leaving the nuclei physically stable, although the nuclear membranes were removed, as shown by electron microscopy. After Triton X-100 treatment, deoxyribonuclease I did not significantly affect the residual NAD+ glycohydrolase activity, although the DNA was completely broken down. This enzyme activity can be released from the nuclear pellet by incubation with phospholipase C. For comparative studies, the glucose 6-phosphatase activity, known to be present in the nuclear envelope, was investigated. Treatment with 0.01% Triton X-100 released 10--20% of the phospholipids, but without solubilizing either glucose 6-phosphatase or NAD+ glycohydrolase. Higher Triton X-100 concentrations (0.1--1.0%) inhibited glucose 6-phosphatase, but not NAD+ glycohydrolase activity. NAD+ glycohydrolase is apparently present in a latent form in the nuclear envelope. Glucose 6-phosphatase, However, shows no such latency.

Animals↗