Reductive nitrosylation of ferric microperoxidase-11

Area of Science:

• Biochemistry
• Chemical Kinetics
• Biophysical Chemistry

Background:

• Microperoxidase-11 (MP11), an undecapeptide from horse heart cytochrome c, serves as a heme-protein model.
• Understanding the reactivity of heme-containing proteins is crucial in various biological processes.

Purpose of the Study:

• To investigate the reductive nitrosylation of ferric MP11 (MP11(III)) under varying pH conditions (7.4–9.2).
• To elucidate the pH-dependent mechanisms of nitric oxide (NO) binding and reaction with MP11.
• To highlight the influence of the protein matrix on heme-based reactivity using MP11.

Main Methods:

• Reductive nitrosylation experiments conducted on MP11(III) under anaerobic conditions.
• Kinetic analysis of NO binding and dissociation over a pH range of 7.4 to 9.2.
• Determination of rate constants (k_on, k_off) and binding constants (K) for MP11(III)-NO complex formation.

Main Results:

• At pH ≤ 7.7, NO reversibly binds to MP11(III) forming MP11(III)-NO.
• Between pH 8.2 and 9.2, MP11(III) is converted to ferrous MP11(II) via a rate-limiting catalytic step, followed by rapid NO binding to form MP11(II)-NO.
• Apparent rate constants for MP11(III)(-NO) (de)nitrosylation are pH-independent, while the rate of MP11{FeNO}⁶ conversion to MP11(II) increases linearly with pH.

Conclusions:

• MP11 exhibits distinct NO binding and reaction pathways dependent on pH.
• The protein matrix plays a significant role in modulating the heme's reactivity, as demonstrated by the pH-dependent catalytic conversion.
• MP11 is a valuable model for studying heme-based redox reactions and the influence of protein environments.