Bariloche protein symposium argentine society for biochemistry and molecular biology

37
BIOCELL, 27 (Suppl. I), 2003
S21.
STRUCTURE AND REGULATION OF NDH COMPLEX
FROM CHLOROPLASTS
Lascano, Hernán Ramiro.
IFFIVE-INTA.Córdoba, Argentina. E-mail: [e-mail]
The plastid Ndh complex, analogous to the Complex I of the
mitochondrial respiratory chain, catalyses the transfer of electrons
from NADH to plastoquinone. The Ndh complex activity together
with Mehler reaction and a plastoquinol peroxidase might poise
the redox level of the photosynthetic electron carriers under
different environmental conditions. Hydrogen peroxide and
calcium mediate plastid-encoded NDH polypeptides and Ndh
complex activity increases under photooxidative stress. Changes
in Ndh complex activity could not only be explained by changes
in Ndh protein levels. The in vivo phosphorylation at threonine
residue(s) of the NDH-F polypeptide was demonstrated in both
thylakoids and immunopurified Ndh complex using monoclonal
phosphoamino acid antibodies. The Ndh complex phosphorylation
level, modulated by H
2
O
2
 and calcium, closely correlated with its
activity. The understanding of the molecular basis of the Ndh
complex function regulation requires structural studies. The
topologies of Ndh complex and its NDH-F subunit were
investigated using bioinformatic tools, proteolitic assays on intact
and permeabilised thylakoids and antibodies against specific
sequences of different NDH subunits. The Ndh complex structure
may be similar to that of respiratory Complex I. NDH-F subunit
would have up to 15 transmembrane helices. The 181-Thr of NDH-
F seems to be the phosphorylation site of Ndh complex since its
highly conserved and is the unique potential Thr phosphorylation
site located in a stromal hydrophilic. Bioinformatic predictions
and the conserved 349-His in the X transmembrane helix, suggest
that NDH-F could be a proton channel.
S22.
PA AND NO ARE TWO SECOND MESSENGERS
INVOLVED IN PLANT-PATHOGEN INTERACTIONS
A. Laxalt, C. de Jong
1
, N. Raho, T. Munnik
1
, L. Lamattina.
IIB, FCEyN, UNMdP, CC 1245, Mar del Plata. Argentina 
1
Plant
Physiology, UVA, The Netherlands.
Nitric oxide (NO) and phosphatidic acid (PA), two emerging
molecules in plant stress signaling, are both involved in the
induction of plant defense. We are interested in how NO and PA
exerts their effect. In the last few years, evidence have been
provided that plant cells contain a variety of phospholipid-based
signaling pathways. These pathways include phospholipase C
(PLC) and D (PLD) activities, which generate the emerging plant
second messenger PA. PA accumulates in tomato cell suspensions
treated with aspecific elicitors such us xylanase, chitotetraose and
flagellin. PA also accumulates in tobacco cells expressing tomato
CF-4
+
 resistance gene treated with the specific C. fulvum elicitor
AVR4. Inhibition of phospholipases responsible for this PA
accumulation, blocks responses associated with plant defense like
the generation of reactive oxygen species (ROS). Moreover,
exogenously applied PA has been shown to generate ROS, which
in turn can induce the hypersensitive response (HR), a form of
programmed cell death (PCD). In animals, NO and ROS act
together triggering PCD. In plants, NO accumulates during plant-
pathogen interactions and inhibitors of NO accumulation
compromise HR and PCD. The first experimental evidence show
that-NO-treated cells accumulate PA, and that xylanase-triggered
PA accumulation depends on the NO presence. This opens an
exciting new field in signal transduction pathways that could drive
plant disease resistance.
Supported by F. Antorchas, CONICET, ANPCyT, UNMdP, TWAS, NWO and
KNAW.
LI-C1.
VANADYL SULFATE, AN INSULIN-MIMETIC, DOES NOT
ALTER UNSATURATED FATTY ACID BIOSYNTHESIS IN
NORMAL OR STREPTOZOTOCIN RATS
Brenner, Rodolfo R.; González, María S.; Basabe, Juan C. and
Bernasconi, Ana M.
INIBIOLP (CONICET-UNLP), Facultad de Ciencias Médicas, La
Plata and CEDIE, Hospital R. Gutiérrez, Buenos Aires, Argentina.
E-mail: [e-mail]
It is widely accepted that Vanadium, either in V
+4
 (vanadyl) or V
+5
salts, shows insulinmimetic properties in experimental animals,
isolated tissues and cell preparations. In streptozotocin (STZ) rats,
Vanadyl normalizes the glycemia and corrects the gene expression
for glucokinase, 6-phosphofructokinase, fatty acid synthetase, etc.
On the other hand, insulin recovers the 
∆9, ∆6 and ∆5 desaturase
activities depressed in insulin-dependent diabetes. In consequence
to compare effects, we examined the action of vanadyl sulfate
added to the drinking water (0.5 g/L  for 1 week, and 1g/L for
three weeks) on control and STZ rats. Glycemia, insulinemia, 
∆6
and 
∆5 desaturase activities, and fatty composition of liver
microsomes were determined. In diabetic rats vanadyl alleviated
the hyperglycemia without modifying the insulinemia. However,
neither the liver 
∆6 and ∆5 desaturation activities nor the fatty
acid composition were altered. Comparing these results to the up-
to-now recognized insulin and vanadium downstream biochemical
events, we may deduce: Vanadyl controls glucose homeostasis,
but undoubtedly it is unable to use the pathways of insulin that
lead to the regulation of the desaturases. The activation of insulin
receptor and insulin receptor tyrosine phosphorylation mechanism
would be essential.
LI-C2.
SELECTIVE PROTECTION OF C20:4 n6 AND C22:6 n3  BY
MELATONIN DURING NON ENZYMATIC LIPID
PEROXIDATION OF RAT LIVER, KIDNEY AND BRAIN
MICROSOMES AND MITOCHONDRIA
Leaden, Patricio and Catalá, Angel.
Cátedra de Bioquímica, Facultad de Ciencias Veterinarias,
Universidad Nacional de La Plata, Argentina. E-mail:
[e-mail]
Melatonin (MLT) (N-acetyl-5-methoxytryptamine), the main
secretory product of the pineal gland, is a free radical scavenger
that has been found to protect against lipid peroxidation in many
experimental models. In the present study the effect of MLT  on
lipid peroxidation of long chain polyunsaturated fatty acids located
in rat liver, kidney and brain microsomes and mitochondria was
determined. The incubation of rat liver, kidney and brain
microsomes or mitochondria in the presence of ascorbate-Fe
2+
resulted in lipid-peroxidation of membranes as evidenced by light
emission and decrease of docosahexaenoic acid 22:6 n-3 and
arachidonic acid 20:4 n-6. In the presence of MLT (0.5, 1.0, 1.5
mM), light emission percent inhibition of microsomes was: (liver-
3.33, 9.98, 39.40) (kidney-46.79, 61.88, 68.36) and (brain-33.36,
28.89, 43.32), whereas light emission percent inhibition of
mitochondria was: (liver-2.74, 19.62, 33.91) (kidney-8.41, 14.66,
44.31) and (brain-4.43, 7.90, 23.55). Not all fatty acids were
equally protected after the addition of melatonin to the incubation
medium. Our results indicate a selective protection of C20:4 n6
and C22:6 n3 by melatonin during non enzymatic lipid peroxidation
of rat liver, kidney and brain microsomes and mitochondria.

---