How azide ion/hydrazoic acid passes through biological membranes

ǂan ǂexperimental and computational study

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

Abstract

Hydrazoic acid (HN3) and its deprotonated form azide ion (N3−) (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 logPe − 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 8.46·104 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.

Keywords

azide ion;hydrazoic acid;octanol/water partition coeficient;efective permeability;PAMPA;difusion;inhibition;cytochrome c oxidase complex IV;

Data

Language:	English
Year of publishing:	2023
Typology:	1.01 - Original Scientific Article
Organization:	KI - National Institute of Chemistry
UDC:	615.4:54:615.9
COBISS:	155988995
ISSN:	1875-8355
Views:	50
Downloads:	10
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	Slovenian
Secondary keywords:	azidni ion;hidrazojska kislina;porazdelitveni koeficient;oktanol/voda;efektivna prepustnost;PAMPA;difuzija;inhibicija;citokrom c oksidazni kompleks IV;Toksini;Farmacevtska kemija;
Type (COBISS):	Article
Pages:	str. 229–238
Issue:	ǂVol. ǂ42
Chronology:	8 Jun. 2023
DOI:	10.1007/s10930-023-10127-3
ID:	19574783