Although the unfolding and refolding of proteins have been extensively studied in tile 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 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 cysteine 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 cysteine residues modified in each subunit of creatine kinase, only three are essential for its folding.
|Number of pages
|Biochemical and Biophysical Research Communications
|Published - Apr 5 1996
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology