The Effect of Dephosphorylation on the Conformation of Peptides from β-Casein

1992 ◽  
Vol 57 (2) ◽  
pp. 425-428
Author(s):  
David C. Clark ◽  
Linda J. Smith ◽  
Lesley C. Chaplin
Keyword(s):  
Alkaline Phosphatase ◽  
Circular Dichroism ◽  
Circular Dichroism Spectra ◽  
Α Helix ◽  
Circular Dichroïsm

Peptides β(1-28) and β(1-52) incorporating residues 1-28 and 1-52 of β-casein were prepared by proteolysis of the protein using plasmin and chymotrypsin respectively. Analysis of the circular dichroism spectra of the isolated peptides revealed that limited levels of α-helix were formed only by peptide β(1-52) and then only in the presence of >40% trifluoroethanol (TFE). Partial dephosphorylation of the peptides by treatment with alkaline phosphatase resulted in the formation of significant levels of α-helix in both peptides in the presence of TFE. However, no α-helix was detected in either peptide in the absence of TFE.

Circular dichroism spectra of adsorbed dye-aggregates

1968 ◽  
Vol 65 ◽  
pp. 146-151 ◽  
Author(s):  
G. Scheibe ◽  
O. Wörz ◽  
F. Haimerl ◽  
W. Seiffert ◽  
J. Winkler
Keyword(s):  
Circular Dichroism ◽  
Circular Dichroism Spectra ◽  
Circular Dichroïsm

Effect of Temperature and pH on the Secondary Structure and Denaturation Process of Jumbo Squid Hepatopancreas Cathepsin D.

2019 ◽  
Vol 26 (7) ◽  
pp. 532-541 ◽  
Author(s):  
Cadena-Cadena Francisco ◽  
Cárdenas-López José Luis ◽  
Ezquerra-Brauer Josafat Marina ◽  
Cinco-Moroyoqui Francisco Javier ◽  
López-Zavala Alonso Alexis ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Secondary Structure ◽  
Cathepsin D ◽  
Thermal Denaturation ◽  
Protein Denaturation ◽  
Marine Organisms ◽  
Effect Of Temperature ◽  
Jumbo Squid ◽  
Α Helix ◽  
Circular Dichroïsm

Background: Cathepsin D is a lysosomal enzyme that is found in all organisms acting in protein turnover, in humans it is present in some types of carcinomas, and it has a high activity in Parkinson's disease and a low activity in Alzheimer disease. In marine organisms, most of the research has been limited to corroborate the presence of this enzyme. It is known that cathepsin D of some marine organisms has a low thermostability and that it has the ability to have activity at very acidic pH. Cathepsin D of the Jumbo squid (Dosidicus gigas) hepatopancreas was purified and partially characterized. The secondary structure of these enzymes is highly conserved so the role of temperature and pH in the secondary structure and in protein denaturation is of great importance in the study of enzymes. The secondary structure of cathepsin D from jumbo squid hepatopancreas was determined by means of circular dichroism spectroscopy. Objective: In this article, our purpose was to determine the secondary structure of the enzyme and how it is affected by subjecting it to different temperature and pH conditions. Methods: Circular dichroism technique was used to measure the modifications of the secondary structure of cathepsin D when subjected to different treatments. The methodology consisted in dissecting the hepatopancreas of squid and freeze drying it. Then a crude extract was prepared by mixing 1: 1 hepatopancreas with assay buffer, the purification was in two steps; the first step consisted of using an ultrafiltration membrane with a molecular cut of 50 kDa, and the second step, a pepstatin agarose resin was used to purification the enzyme. Once the enzyme was purified, the purity was corroborated with SDS PAGE electrophoresis, isoelectric point and zymogram. Circular dichroism is carried out by placing the sample with a concentration of 0.125 mg / mL in a 3 mL quartz cell. The results were obtained in mdeg (millidegrees) and transformed to mean ellipticity per residue, using 111 g/mol molecular weight/residue as average. Secondary-structure estimation from the far-UV CD spectra was calculated using K2D Dichroweb software. Results: It was found that α helix decreases at temperatures above 50 °C and above pH 4. Heating the enzyme above 70°C maintains a low percentage of α helix and increases β sheet. Far-UV CD measurements of cathepsin D showed irreversible thermal denaturation. The process was strongly dependent on the heating rate, accompanied by a process of oligomerization of the protein that appears when the sample is heated, and maintained a certain time at this temperature. An amount typically between 3 and 4% α helix of their secondary structure remains unchanged. It is consistent with an unfolding process kinetically controlled due to the presence of an irreversible reaction. The secondary structure depends on pH, and a pH above 4 causes α helix structures to be modified. Conclusion: In conclusion, cathepsin D from jumbo squid hepatopancreas showed retaining up to 4% α helix at 80°C. The thermal denaturation of cathepsin D at pH 3.5 is under kinetic control and follows an irreversible model.

scholarly journals Natural and magnetic circular dichroism spectra of nucleosides: effect of the dynamics and environment

RSC Advances ◽  
2021 ◽  
Vol 11 (14) ◽  
pp. 8411-8419
Author(s):  
Jakub Kaminský ◽  
Valery Andrushchenko ◽  
Petr Bouř
Keyword(s):  
Molecular Dynamics ◽  
Circular Dichroism ◽  
Nucleic Acids ◽  
Electronic Absorption ◽  
Magnetic Circular Dichroism ◽  
Circular Dichroism Spectra ◽  
Circular Dichroïsm ◽  
Magnetic Circular Dichroism Spectra

Electronic absorption, natural and magnetic circular dichroism spectra of several nucleosides are simulated to understand their dependence on molecular dynamics and environment, their sensitivity to nucleoside pairing and stacking in nucleic acids.

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