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Reactivity of Singlet Oxygen Toward Proteins: The Effect of Structure in Basic Pancreatic Trypsin Inhibitor and in Ribonuclease A
Author(s) -
Michaeli Albert,
Feitelson Jehuda
Publication year - 1997
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1997.tb08563.x
Subject(s) - bovine pancreatic ribonuclease , chemistry , rnase p , ribonuclease , singlet oxygen , quenching (fluorescence) , amino acid , trypsin , denaturation (fissile materials) , pancreatic ribonuclease , trypsin inhibitor , biochemistry , enzyme , oxygen , organic chemistry , fluorescence , rna , nuclear chemistry , physics , quantum mechanics , gene
The reactions of singlet oxygen, 1 O 2 , with large peptides have been described previously. It was found that even in these systems, which in their native form are generally not supposed to possess a stable structure in solution, the polypeptide does impede the access of 1 O 2 to the amino acids that react readily with 1 O 2 . Here we describe the 1 0 2 reaction with two proteins of well‐defined structure. The quenching of 1 O 2 by bovine pancreatic trypsin inhibitor (BPTI) and by ribonuclease A (RNase A) was compared to that of a solution at the same concentration as those of its constituent amino acids that react readily with 1 O 2 . The proteins were studied in their native form, when partly denatured by splitting their S‐S bonds and when fully denatured. It was found that while in the native form the quenching rate constant was seven times lower in BPTI (2.2 vs 15.2 times 10 7 WM ‐1 s ‐1 ) and three times lower in RNase A (11.0 vs 32 times 10 7 M ‐l s ‐1 ) than in a mixture of its constituent amino acid residues, it increased upon denaturation reaching in the fully denatured state the value of the corresponding amino acid mixture. More striking is the effect of the protein structure when comparing the fraction of the encounters between 1 O 2 and protein, which cause damage to the protein, as reflected in the decrease of its biological activity. This decrease is assumed to be due to the chemical (oxidative) reactions of 1 O 2 in the protein. In the exceptionally stable BPTI the fraction of such encounters was 0.05 and in RNase A it was 0.2, whereas for the amino acid tryptophan in solution, 0.7 of the collisions with 1 O 2 led to a chemical reaction.