Biomedical subjects

M L Bonet

Publications and source records attributed to M L Bonet.

22 records · Page 2Linked to original sources

PubMed1992

The catalytic site is located on subunit I of the ATPase from Halobacterium saccharovorum. A direct photoaffinity labeling study.

Nucleotide-binding sites of the ATPase from the halophilic archaebacterium Halobacterium saccharovorum were labeled by ultraviolet irradiation in the presence of [alpha-32P]ATP. A high-affinity site, located on subunit I (98 kDa), was identified as catalytic by the following criteria: ATP bound to subunit I was hydrolyzed and the cross-linked nucleotide was ADP; the specificity for ATP or ADP compared to that of other nucleotides was high; the tightly bound radionucleotide was exchangeable in the presence of excess unlabeled ATP and Mg2+; photolabeling of this site and enzyme inhibition due to tightly bound ADP were both dependent on the presence of Mg2+ and showed identical Kd values; treatment that restored the activity of the ADP-inhibited enzyme also led to the release of the tightly bound nucleotide from subunit I. In addition, a non-catalytic nucleotide-binding site was found, located on subunit II (71 kDa). This site did not hydrolyze ATP, its occupation was Mg2+ independent and the affinity for ATP and the nucleotide specificity were much lower than that of subunit I. We suspect that this site is nonspecific. These results indicate that H. saccharovorum ATPase is different from F1-ATPases which contain the catalytic site on the second largest subunit, but may be similar to other archaebacterial and vacuolar ATPases.

Adenosine Triphosphatases↗

PubMed1992

Alkaline p-nitrophenylphosphate phosphatase activity from Halobacterium halobium. Selective activation by manganese and effect of other divalent cations.

1. Alkaline p-nitrophenylphosphate phosphatase (pNPPase) activity of Halobacterium halobium is selectively stabilized and stimulated by Mn2+ ions. 2. Mn2+ binding to native pNPPase is characterized by a dissociation constant of 0.35 mM at pH 8.5, 37 degrees C, with a Hill coefficient of 0.988. 3. Mn2+ behaves as a mixed type nonessential activator, increasing the Vmax value (beta = 6.09, pH 8.5) and decreasing the Km value for pNPP (alpha = 0.56, pH 8.5). The Ki value for inorganic phosphate (a competitive inhibitor) was also decreased in the presence of Mn2+. 4. Activation of native pNPPase by preincubation with Mn2+ is a slow temperature-dependent process, which can be described by an exponential relationship vs time. However, a weak but immediate activation was also detected. 5. Zn2+, Cu2+ and Ni2+ were found to inhibit both native and Mn(2+)-stimulated pNPPase, whereas Co2+ and Cd2+ inhibited the Mn(2+)-stimulated pNPPase but had no effect on the native enzyme form.

4-Nitrophenylphosphatase↗

PubMed1992

Involvement of thiol groups in the reaction mechanism of Mn(2+)-activated alkaline p-nitrophenylphosphate phosphatase of the extreme halophilic archaebacterium Halobacterium halobium.

Halobacterium halobium contains a cytosolic alkaline p-nitrophenylphosphate phosphatase which is selectively activated by Mn2+ ions (Bonet et al., 1991: Int. J. Biochem. 12, 1445-1451). We investigated the reaction mechanism of the enzyme in the presence and the absence of Mn2+ by means of pH studies and the application of some group-specific reagents. A pKes 8.4 of a group in the Mn(2+)-enzyme-substrate complex involved in catalysis could not be detected when catalysis in the absence of the cation was analysed. Only the enzyme with bound Mn2+ was inhibited by p-hydroxymercuribenzoate. Reducing agents stimulated the Mn(2+)-dependent activity but had no effect on the native enzyme activity. Our results indicate that the reaction mechanism is different whether the activating cation is present or not, and that the reaction mechanism in the presence of Mn2+ involves thiol groups.

4-Nitrophenylphosphatase↗

PubMedDate not supplied

[Nutrigenomics and obesity].

Obesity is a multifactorial disorder affected by multiple genetic and environmental factors, in particular nutrients, and their interrelationships. Increasing knowledge of the genes and molecules involved in the development of obesity is paving the way for new methods of obesity control. In this sense, Nutrigenomics--which represents a new approach in nutrition research that joints the application of powerful functional genomics technologies, bioinformatics and molecular biology with more traditional methodologies--may orientate the design and development of new functional foods for obesity, based on the scientific knowledge of the impact of specific nutrients on the mammalian body weight control system and their mechanisms of action.

Adipocytes↗