Water-soluble lysine-containing polypeptides. V. Circular dichroisrm, electron microscopic, and thermal denaturation studies of the interaction of poly(L-lysyl-L-alanine) and poly(L-lysyl-D-alanine) with calf thymus DNA

1978 ◽  
Vol 56 (20) ◽  
pp. 2650-2656 ◽  
Author(s):  
Sandra L. Kielland ◽  
Lewis A. Slotin ◽  
Ross E. Williams
Keyword(s):  
Circular Dichroism ◽  
Secondary Structure ◽  
Electron Micrographs ◽  
Thermal Denaturation ◽  
Water Soluble ◽  
Calf Thymus Dna ◽  
Circular Dichroism Spectra ◽  
Electron Microscopic ◽  
Calf Thymus ◽  
Circular Dichroïsm

Turbidity measurements, circular dichroism spectra, electron micrographs and thermal denaturation profiles of complexes between sonicated DNA and either poly(L-lysyl-L-alanine) or poly(L-lysyl-D-alanine) show significant differences which might be related to the primary or secondary structure of the polypeptides.

Water-soluble lysine-containing polypeptides. VI. A study of annealed complexes between calf thymus DNA and the following copolymers: poly-(L-lysyl-X), where X = Gly, L-Ala, L-Val, L-Leu, and L-Phe

1978 ◽  
Vol 56 (20) ◽  
pp. 2657-2664 ◽  
Author(s):  
Sandra L. Kielland ◽  
Lewis A. Slotin ◽  
Ross E. Williams
Keyword(s):  
Electron Micrographs ◽  
Water Soluble ◽  
Optical Measurements ◽  
Calf Thymus Dna ◽  
Synthetic Route ◽  
Circular Dichroism Spectra ◽  
Chain Branching ◽  
Calf Thymus ◽  
Polypeptide Synthesis ◽  
Circular Dichroïsm

Turbidity measurements, circular dichroism spectra, electron micrographs, and thermal–optical measurements have been made on complexes between sonicated DNA and several polypeptides with the following structure: poly-(L-lysine-L-X) where X = Gly, Ala, Val, Leu, Phe. The results are influenced by any method of polypeptide synthesis which results in chain branching of the polypeptide. When polypeptides prepared by the same synthetic route are incorporated into the complexes the results also depend on the polypeptide used. Five possible explanations are offered as sources of the latter observations.

Water-soluble lysine-containing polypeptides. IV. The synthesis, characterization,and circular dichroism spectra of sequential polypeptides formed from dipeptides of lysine and amino acids of increasing side chain size

1977 ◽  
Vol 55 (24) ◽  
pp. 4257-4266 ◽  
Author(s):  
Lewis A. Slotin ◽  
Denis R. Lauren ◽  
Ross E. Williams
Keyword(s):  
Amino Acids ◽  
Molecular Weight ◽  
Circular Dichroism ◽  
Secondary Structure ◽  
Gel Filtration ◽  
Circular Dichroism Spectroscopy ◽  
Water Soluble ◽  
Side Chain ◽  
Circular Dichroism Spectra ◽  
Circular Dichroïsm

Several polypeptides have been synthesized which contain the alternating sequence lysyl-X, where X = gly, L-ala, D-ala, L-val, L-leu, and L-phe. The polypeptides have been characterized by gel filtration (molecular weight) and by circular dichroism spectroscopy (secondary structure).

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.

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