How azide ion/hydrazoic acid passes through biological membranes : an experimental and computational study

Lojevec Hartl, Simona (author), Žakelj, Simon (author), Sollner Dolenc, Marija (author), Smrkolj, Vladimir (author), Mavri, Janez (author)

Hydrazoic acid (HN$_3$) and its deprotonated form azide ion (N$_3$$^−$) (AHA) are toxic because they inhibit the cytochrome c oxidase complex IV (CoX IV) embedded in the inner mitochondrial membrane that forms part of the enzyme complexes involved in cellular respiration. Critical to its toxicity is the inhibition of CoX IV in the central nervous system and cardiovascular system. Hydrazoic acid is an ionizable species and its affinity for membranes, and the associated permeabilities, depend on the pH values of aqueous media on both sides of the membranes. In this article, we address the permeability of AHA through the biological membrane. In order to understand the affinity of the membrane for the neutral and ionized form of azide, we measured the octanol/water partition coefficients at pH values of 2.0 and 8.0, which are 2.01 and 0.00034, respectively. Using a Parallel Artificial Membrane Permeability Assay (PAMPA) experiment, we measured the effective permeability through the membrane, which is logP$_e$ − 4.97 and − 5.26 for pH values of 7.4 and pH 8.0, respectively. Experimental permeability was used to validate theoretical permeability, which was estimated by numerically solving a Smoluchowski equation for AHA diffusion through the membrane. We demonstrated that the rate of permeation through the cell membrane of 8.46·10$^4$ s$^{-1}$ is much higher than the rate of the chemical step of CoX IV inhibition by azide of 200 s$^{-1}$. The results of this study show that transport through the membrane does not represent the rate-limiting step and therefore does not control the rate of CoX IV inhibition in the mitochondria. However, the observed dynamics of azide poisoning is controlled by circulatory transport that takes place on a time scale of minutes.

• Language: English
• Keywords: azide ion, hydrazoic acid, octanol/water partition coefficient, effective permeability, PAMPA, diffusion, inhibition, cytochrome c oxidase complex IV
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FFA - Faculty of Pharmacy; MF - Faculty of Medicine
• Publication status: Published
• Publication version: Version of Record
• Year: 2023
• Number of pages: Str. 229–238
• Numbering: Vol. 42, iss. 3
• PID: 20.500.12556/RUL-147004
• UDC: 615.4:54:615.9
• ISSN on article: 1875-8355
• DOI: 10.1007/s10930-023-10127-3
• COBISS.SI-ID: 155988995
• Publication date in RUL: 17.07.2023

Record is a part of a journal

• Title: The protein journal
• Publisher: Springer Nature
• ISSN: 1875-8355
• COBISS.SI-ID: 527281689

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: azidni ion, hidrazojska kislina, porazdelitveni koeficient, oktanol/voda, efektivna prepustnost, PAMPA, difuzija, inhibicija, citokrom c oksidazni kompleks IV, toksini, farmacevtska kemija

Projects

• Funder: ARRS - Slovenian Research Agency
• Project number: P1-0012
• Name: Molekulske simulacije, bioinformatika in načrtovanje zdravilnih učinkovin