Biology Reference
In-Depth Information
stand out, describing the properties of FHb from the bacterium
Alcaligenes
eutrophus
(the name later changing to
Ralstonia eutrophus
then
Wausteria
eutrophus
, and now
Ralstonia metallidurans
or
Cuprivadus necator
) and the bud-
ding yeast
Candida mycoderma
. Earlier, however, in the early 1970s, Chance
and the Oshinos described the purification of a 'yeast haemoglobin-
reductase complex' (
Oshino, Asakura, Tamura, Oshino, & Chance, 1972
)
from
C
.
mycoderma
in which haem and flavin were associated with a single
polypeptide reducible by NAD(P)H. Subsequent characterization revealed
its oxygen affinity and other properties (
Oshino, Asakura, et al., 1973;
Oshino, Oshino, &Chance, 1971, 1973
) but no clear physiological function
emerged. A similar protein was purified from
Ralstonia
(
Probst & Schlegel,
1976; Probst, Wolf, & Schlegel, 1979
) and this protein was later to become
the first FHb for which a crystal structure would be solved (
Ermler, Siddiqui,
Cramm, & Friedrich, 1995
).
The literature on yeast globins (YHbs) is extensive yet not always clear
regarding protein function. Chance and co-workers did not propose a role
in NO biochemistry as is generally accepted now. They were able, however,
to demonstrate a robust NADH oxidation rate (
Oshino, Asakura, et al.,
1973; Oshino et al., 1971
), which is a hallmark of the FHb-catalysed
NO detoxification reaction of bacteria (
Mills, Sedelnikova, Soballe,
Hughes, & Poole, 2001; Poole, Ioannidis, & Orii, 1994
). Most studies have
been conducted on non-pathogenic yeasts, particularly
Saccharomyces
cerevisiae
but also
Candida
species (
Kobayashi et al., 2002
). Prior to the dis-
covery of the up-regulation of
hmp
gene expression in
Escherichia coli
by NO
(
Poole et al., 1996
) and the demonstration of NO consumption,
Crawford,
Sherman, and Goldberg (1995)
had studied
S
.
cerevisiae
haemoglobin expres-
sion ('YHG') and found it to be induced during logarithmic growth and
under oxygen-replete conditions. At the time, this was considered to mark
a clear distinction from the only bacterial globin that had been studied in
depth, namely the
Vitreoscilla
case (
Dikshit, Spaulding, Braun, & Webster,
1989; Lamba &Webster, 1980
). However, we now know that FHbs in bac-
teria are also expressed during aerobic growth. Although
Crawford et al.
(1995)
also tested the effects of gene disruption and found no phenotype
(growth, viability) under a variety of growth conditions and with various
carbon sources, no clues to function emerged.
Zhao et al. (1996)
showed
that intracellular levels of the YHb were greatly increased in cells in which
mitochondrial electron transport was impaired and demonstrated maximal
expression under hypoxic and anoxic conditions. The response of a
YHB1
deletion mutant to NO was not tested but the mutant was sensitive
