Biomedical Engineering Reference
In-Depth Information
8.6 Applications of polarographic H
2
S sensors in biological samples
8.6.1 Measurement of H
2
S production
8.6.1.1 Tissue homogenates
8.6.1.2 Cultured and isolated cells
8.6.1.3 Intact tissues and organs
8.6.2 Measurement of H
2
S consumption
8.6.2.1 Isolated mussel gill mitochondria
8.6.2.2 Cultured cells, intact tissues and organs
8.6.3 Simultaneous measurement of H
2
S level and vessel tension
8.6.4 Measurement of steady-state H
2
S levels in blood and tissue
8.7 Concluding remarks and future directions
8.8 Acknowledgments
8.9 References
8.1 INTRODUCTION
Hydrogen sulfi de (H
2
S) is most commonly known as a toxic gas with the repulsive
odor of rotten eggs. Although H
2
S can be toxic through its inhibitory interactions with
hemoglobin and cytochrome
c
oxidase [1, 2], many prokaryotic and eukaryotic organ-
isms thrive in sulfi dic habitats and have been shown to possess putative H
2
S oxidases
and alternative oxidases that operate in concert with mitochondria to gain energy from
H
2
S oxidation as well as to prevent inhibition of aerobic metabolism [3, 4]. In addi-
tion, micromolar tissue H
2
S levels have been observed in animals from H
2
S-free envi-
ronments [5, 6] as well as in human brain tissue and blood [7-9], suggesting that H
2
S
is a constituent of the cellular milieu.
H
2
S can be produced via the metabolism of sulfhydryl-bearing amino acids, specifi -
cally by several enzymes found in the methionine-homocysteine-cysteine pathway such
as cystathionine
lyase (CGL) (Fig. 8.1) [6, 10, 11].
The sequence of CBS has been identifi ed in genomes from bacteria to humans [12-14],
and a gene similar to the sulfi de:quinone oxidoreductase gene has been identifi ed in the
genome of fl ies, worms, mice, rats, and humans [15], indicating that cellular H
2
S and its
regulation may be widespread and essential.
The apparent paradox of a toxic molecule in living aerobic tissues has precedent in
the presence of other small rapidly diffusing molecules that are both critical in cell sig-
naling and also potentially toxic, namely nitric oxide (NO) and carbon monoxide (CO).
In the past two decades, the demonstration that NO is a critically important biological
molecule has greatly expanded our understanding of cell signaling. H
2
S shares many
properties with NO, and the potential for H
2
S to participate in cell signaling is clear.
However, its broader biological role is not well understood partially as a result of the
lack of sensitive and specifi c methods for the real time measurement of this molecule
in complex biological milieu. In this review, we describe a novel polarographic H
2
S
β
synthase (CBS) and cystathionine
γ
Search WWH ::
Custom Search