Biomedical subjects

S Y Zheng

Publications and source records attributed to S Y Zheng.

12 recordsLinked to original sources

PubMed2001

[Experimental research of protective and therapeutic effects of zinc and vitamin E on mouse liver radiational damage].

OBJECTIVE: To study the effects of zinc and vitamin E on lipid peroxide (LPO) contents and glutathione peroxidase (GSH-Px) activities in liver homogenates of radiational damage mice. METHODS: Two hundred and forty mice were divided randomly into five groups: normal control group (Group A), 60Co gamma-ray irradiator group (Group B), 60Co + zinc (Zn) group (Group C), 60Co + vitamin E(VE) group (Group D), and 60Co + Zn + VE group (Group E). After irradiated with 60Co gamma-ray 7.5 Gy, the mice were protectively treated with Zn and VE at different times. LPO contents and GSH-Px activities in liver homogenates of the mice were determined. RESULTS: The level of liver LPO was significantly higher (P < 0.01), but the level of liver GSH-Px was significantly lower (P < 0.01) in Group B than those in Group A; the content of liver GSH-Px was markedly higher in Group C and Group D than that in Group B (P < 0.01), while the content of liver LPO was markedly lower in Group D than that in Group B (P < 0.05); the concentration of liver GSH-Px was markedly higher in Group E than that in Group D (P < 0.01). CONCLUSIONS: VE may play an important role in lowering liver LPO contents and raising liver GSH-Px activities in radiational damage mice. vitamin E can cooperate with zinc in raising liver GSH-Px activities, stopping liver cells from lipids peroxidation and keeping integrity of liver cell membrane.

Animals↗

PubMed1999

Evidence for the existence of an unfolding intermediate state for aminoacylase during denaturation in guanidine solutions.

The equilibrium unfolding of pig kidney aminoacylase in guanidinium chloride (GdmCl) solutions was studied by following the fluorescence and circular dichroism (CD). At low concentrations of GdmCl, less than 1.0 M, the fluorescence intensity decreased with a slight red shift of the emission maximum (from 335 to 340 nm). An unfolding intermediate was observed in low concentrations of denaturant (between 1.2 and 1.6 M GdmCl). This intermediate was characterized by a decreased fluorescence emission intensity, a red-shifted emission maximum, and increased binding of the fluorescence probe 1-anilino-8-naphthalenesulfonate. No significant changes of the secondary structure were indicated by CD measurement. This conformation state is similar to a molten globule state which may exist in the pathway of protein folding. Further changes in the fluorescence properties occurred at higher concentrations of GdmCl, more than 1.6 M, with a decrease in emission intensity and a significant red shift of the emission maximum from 340 to 354 nm. In this stage, the secondary structure was completely broken. A study of apo-enzyme (Zn2+-free enzyme) produced similar results. However, comparison of the changes of the fluorescence emission spectra of native (Holo-) enzyme with Zn2+-free (Apo-) enzyme at low GdmCl concentrations showed that the structure of the Holo-enzyme was more stable than that of the Apo-enzyme.

Amidohydrolases↗

PubMed1998

Inactivation of creatine kinase is due to the conformational changes of the active sites during thermal denaturation.

The conformational changes of the active site of creatine kinase (ATP: creatine N-phosphotransferase EC 2.7.3.2.) during thermal denaturation was followed by changes in fluorescence at the active site of the enzyme labeled by o-phthalaldehyde. Conformational changes of the active site occurred at the same time as inactivation of the enzyme. The active site changes occurred before the denaturation of the enzyme molecule as a whole was detected. The above results showed that the thermal inactivation of the creatine kinase was due to the conformational changes of its active sites.

Binding Sites↗

PubMed1997

Kinetics of irreversible inhibition of yeast alcohol dehydrogenase during modification by 4,4'-dithiodipyridine.

The course of inactivation of yeast alcohol dehydrogenase (YADH) using 4,4'-dithiodipyridine (DSDP) has been studied in this paper. The results show that the reaction mechanism between DSDP and YADH is a competitive, complexing inhibition. The microscopic constants for the inactivation of the free enzyme and the enzyme-substrate complex were determined. The presence of the substrate NAD+ offers strong protection for this enzyme against inactivation by DSDP. The above results suggest that two Cys residues are essential for activity and are situated at the active site. These essential Cys residues should be Cys-46 and Cys-174 which are ligands to the catalytic zinc ion. Another Cys residue, which can be modified by DSDP, is non-essential for activity of the enzyme.

Alcohol Dehydrogenase↗

PubMed1996

Ascertaining the number of essential thiol groups for the folding of creatine kinase.

Although the unfolding and refolding of proteins have been extensively studied in the literature, relatively few attempts have been made to see how many residues of the total residues of a certain amino acid in an enzyme can be modified without seriously affecting its folding. Based on a statistical analysis of the quantitative relationship between the extent of modification of protein functional groups and the decrease in their biological activity, a method proposed by Tsou (Sci. Sin. 1962, 11, 1535-1558) is widely used to determine the number of residues essential for the catalytic activity of modified proteins. In the present paper, Tsou's method is applied to determine the number of cystein residues essential for the folding of creatine kinase. The thiol groups of the cysteine residues in fully unfolded creatine kinase were modified by 2-chloromercuri-4-nitrophenol (MNP). The relationship between the number of MNP-groups introduced and the recovery of activity after refolding was determined. Quantitative treatment of the data by Tsou's plot shows that among the cystein residue modified in each subunit of creatine kinase, only three are essential for its folding.

Animals↗

PubMed1988

Immunoprecipitation of the in vitro translation product of rabbit muscle protein phosphatase C-I mRNA.

Rabbit muscle polyA+ mRNA was translated in vitro using a rabbit reticulocyte lysate system in the presence of [35S]methionine. A mouse monoclonal antibody to the catalytic subunit of rabbit muscle phosphorylase phosphatase ("phosphatase C-I") was used to immunoprecipitate the products which were then analyzed by SDS-PAGE and autoradiography. These studies showed that the major product of the phosphatase mRNA is a single ca. 36 kDa polypeptide. These findings are significant in view of suggestions that the catalytic subunit is derived from a larger precursor, and in view of the molecular cloning of two cDNAs for the phosphatase, which encode polypeptides of 35.4 kDa and 37.5 kDa, respectively.

Animals↗

PubMed1986