Alkaline isomerization of horse and yeast cytochromes C. Spectrophotometric and circular dichroism studies.

The article presents the analysis of how alkaline (a base substance) affects the isomerization (changes in molecular structure) of cytochromes c (proteins involved in cell energy production) from horse heart and yeast cells. Distinct variations were found between the yeast proteins and the mammalian proteins under differing pH levels.

Objective of the Study

• The study aims to investigate the impact of alkaline conditions on the isomerization of cytochrome c in horse and yeast.
• The research explores the differing responses between yeast and mammalian cytochrome c, using spectrophotometric and circular dichroism methods.

Spectrophotometric Studies

• Spectrophotometry is a method used to measure the amount of light absorbed by a substance. In this case, it helped determine the effects of alkalinity on the cytochrome c’s structural transformation.
• The scientists measured the decrease in absorbance at 695 nm as the pH increased, allowing them to understand how isomerization processes change under alkaline conditions.

Circular Dichroism Studies

• Circular dichroism is a technique that measures the difference in absorption of left and right circularly polarized light. This study used it to verify whether the results from the spectrophotometric studies correlate to structural changes in the proteins.
• The study found a decrease in the negative circular dichroism band centered at 417 nm, providing additional proof of the changes in the protein structures.

Findings

• The apparent pKa values (used to measure acidity or alkalinity) of isol-1 (both methylated and unmethylated forms) and iso-2-cytochrome c from baker’s yeast were found to be 8.41, 8.40, and 8.73 respectively. These differ significantly from the pKa value of horse heart cytochrome c which was 9.40.
• These findings give further evidence that the ligation of the heme iron by the sulfur atom of methionine 8u is closely involved in the structure of each of the four hemoproteins examined.