ISSN 10214437, Russian Journal of Plant Physiology, 2011, Vol. 58, No. 1, pp. 181–184. © Pleiades Publishing, Ltd., 2011.
Plastocyanin (PC) is a Cucontaining protein with
a mol. wt of
kD. Initially, it has been isolated
from the green alga
. Later, PC
has been identified in higher plants, many green algae,
and some cyanobacteria . PC takes part in the pho
tosynthetic electron transport chain between photo
system II (PSII) and photosystem I (PSI); it is a natu
ral electron donor of PSI . PC is weakly bound to
the membrane and freely diffuses in the lumen [3, 4].
PC is the most investigated cupredoxin . As a typi
cal cupredoxin, PC possesses the characteristic for this
protein family conservative globular
wich” structure. It includes two acidic clusters in the
“eastern” region of the globule and one Cuactive site
in the “northern” hydrophobic region, which is
important for the physiological electron transfer func
tion. The Cu atom is coordinately bound to
ing a distorted tetrahedron .
In the schemes of the photosynthetic chain, PC is
still indicated as a homogeneous protein with one
polypeptide chain of about 99 amino acid residues .
Our investigations, however, have shown the presence
This text was submitted by the authors in English.
of a second PC molecule as a structural isomer of the
wellknown PC. It was denoted as
to keep it dis
tinct from the already known isoform denoted as PC
. A series of physicochemical and structural studies
revealed essential differences between the two PC iso
forms , which could be a prerequisite for specific
different roles of PC
in the photosynthesis.
After finding out the genes of the two PC isoforms
in the nuclear genome of
interest in the problem concerning the physiological
role of the PC dimorphism increased. Weigel et al. 
have shown that mutations of each of the two
PC genes damaged the growth and devel
opment of the plant, making it feeble and stunted.
Under the same experimental conditions, the simulta
neous mutation of the two genes was lethal for the
plant. Two homologous plastocyanin isoforms are
encoded by the genes
Recently, some new interpretations concerning the
functions of the two PC isoforms have been submitted.
Pesaresi et al.  have revealed that null mutations in
genes have resulted in
with decreased PC contents (by 20–40 and over 90%,
null mutation affected
the rate of photosynthesis and slightly suppressed
plants did not show any alter
ations. These researchers have concluded that PC
concentration is not limiting for the overall photosyn
thetic electron flow. However, they do not exclude
Changes in the Content of Poplar Isoplastocyanins
during Vegetation Cycle
M. I. Dimitrov, A. A. Donchev, A. Ch. Shosheva, V. I. Getov, N. P. Terezova, and S. D. Stoichev
Institute of Biophysics, Bulgarian Academy of Sciences, Acad. G. Bonchev str., Bl. 21,1113Sofia, Bulgaria;
fax: +35929712493; email: email@example.com
Received November 12, 2009
—Changes in the content of isoplastocyanins
leaves were stud
ied during complete vegetation cycle (from April 30 to October 28). Measurements were made every 7 days.
The procedure included extraction and purification of total protein followed by analytical isoelectric focusing
and densitometry of obtained isophoregrams. The positions of PC
were determined by comparison
with the positions of the highly purified two isoforms. The PC
ratio was calculated from the areas of
the corresponding densitometric peaks. The amount of PC
was one half of PC
amount in the earliest stage
of the leaf formation as well as during the longer part of the summer, e.g., the second half of July, August, and
September. During the most active period of the poplar growth, e.g., June and the first half of July, the ratio
was about or above unity. This result could be important for understanding the specific functional significance
Keywords: Populus nigra
, photosynthesis, plastocyanin, dimorphism, anionexchange chromatog
raphy, isoelectric focusing, densitometry.
IEF—isoelectric focusing; PC—plastocyanin;
PMSF—phenylmethylsulphonyl fluoride; PSII—photosystem
II; PSI—photosystem I.