3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
these enzyme forms in individual cell structures was determined
using the differential centrifugation method 5 .
Results
Only pectate hydrolases with terminal action pattern
on substrate were found in parsley roots cells 6,7 . ExoPG and
two types of OGH were isolated, partially purified, further
characterized and in-between compared. The comparison of
their molecular masses, isoelectric points (Table I), temperature
optima, thermal stability and also action pattern showed
very similar results. On the other hand there were observed
differences in their pH optima (Fig. 1., Table I) and substrate
specificity in respect to DP of substrate (Fig. 2., Table I). In
addition, the individual enzyme forms occurred in different
cell structures as is partially shown (Fig. 3.).
Fig. 2. The initial rates of pectate hydrolases from parsley
roots on substrates with various DP: A – enzymes isolated from
parsley juice with ph optimum 3.6 – �, 4.2 – �, 4.6 – � and 5.2
– �, b – enzyme found in parsley pulp with ph optimum 4.7
Table I
Characterization of pectate hydrolases from parsley root
cells
Enzyme
DP of
pH
optimum preferred
substrate
A
B
M r pI Occurrence
OGH6a 3.6 6 55.3 5.45 organelles
OGH6b 4.2 6 55.3 5.35 plasts, walls
OGH6c 4.6 6 55.3 5.60 intracel. comp.
OGH10 4.7 10 53.5 5.30 wall
exoPG 5.2 PGA 55.3 5.55 wall, ER
s631
Fig. 3. Abundance of individual exopectate hydrolase activities
in different cell component: A – cell wall, b – cytosol
ExoPG preferring the polymeric substrate has its pH
optimum at 5.2. In contrast, the other types of pectate hydrolases,
OGHs, favour oligomeric substrates, hexagalacturonate
(OGH6) and decagalacturonate (OGH10) respectively.
OGH10 has its pH optimum at 4.7.
OGH6 includes three isoforms with pH optima at 3.6,
4.2 and 4.6 (Table I). All forms showed temperature optima
between 60–70 °C and were 100% stable at 55 °C (all
unbound forms) and 50 °C (OGH10) respectively.
Conclusions
Five forms of pectate hydrolases purified from parsley
root cells were described 6,7 . The main difference between
these enzymes is mainly the substrate preference in relation
to the chain length. It is accompanied by the sharp decrease
of pH optima with decrease in DP of preferred substrate.
The relationship between pH decrease in primary cell wall
during auxin activation of proton pump bound on plasmatic
membrane 8 and DP decrease in linear parts of pectin molecule
side chains 9 regulated by pectate hydrolases with terminal
action pattern can be indicated.
One enzyme only (OGH10), with preference to decameric
substrate, was strictly bound to the cell wall. next three
forms, with preference to hexagalacturonate, were found in
other cell structures. Only one typical form of exoPG with
preference to polymeric substrate was identified; partially
bound to the cell wall and partially free in the cytosol.
A
B