Enzymes, Caspases, Cysteine Proteasis, Radiation, Inflammation, Acute Radiation Disease, Acute Radiation Syndromes.

1. RADIATION TOXICITY:
HYDROLYTIC ENZYMES –
CYSTEINE_PROTEASES.
Dmitri Popov. PhD, Radiobiology. MD (Russia)
Advanced Medical Technology and Systems Inc.
Canada.

2. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 A lysosome (derived from the Greek words lysis,
meaning "to loosen", and soma, "body") is
a membrane-bound cell organelle found in most
animal cells (they are absent in red blood cells).
Structurally and chemically, they are spherical
vesicles containing hydrolytic enzymes capable of
breaking down virtually all kinds of biomolecules,
including proteins, nucleic acids,
carbohydrates, lipids, and cellular debris. They are
known to contain more than 50 different enzymes,
which are all optimally active at an acidic
environment of about pH 5.
http://en.wikipedia.org/wiki/Lysosome

3. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 Thus lysosomes act as the waste disposal
system of the cell by digesting unwanted
materials in the cytoplasm, both from outside
of the cell and obsolete components inside the
cell. For this function they are popularly
referred to as "suicide bags" or "suicide sacs"
of the cell.
http://en.wikipedia.org/wiki/Lysosome

4. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 Cysteine proteases, also known as thiol
proteases, are enzymes that
degrade proteins. These proteases share a
common catalytic mechanism that involves
a nucleophilic cysteine thiol in a catalytic
triad or dyad. The first step in the reaction
mechanism by which cysteine proteases
catalyze the hydrolysis of peptide bonds is de
protonation of a thiol in the enzyme's active
site by an adjacent amino acid with a
basic side chain, usually a histidineresidue.

5. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 The next step is nucleophilic attack by
the deprotonated cysteine's anionic sulfur on
the substrate carbonyl carbon. In this step, a
fragment of the substrate is released with
an amine terminus, the histidine residue in
the protease is restored to its deprotonated
form, and a thioester intermediate linking the
new carboxy-terminus of the substrate to the
cysteine thiol is formed.
 http://en.wikipedia.org/wiki/Cysteine_protease

6. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 Therefore they are also sometimes referred to
as thiol proteases. The thioester bond is
subsequently hydrolyzed to generate
a carboxylic acid moiety on the remaining
substrate fragment, while regenerating the free
enzyme.
 http://en.wikipedia.org/wiki/Cysteine_protease

7. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 Cysteine proteases play multi-faceted roles,
virtually in every aspect of physiology and
development. In plants they are important in
growth and development and in accumulation
and mobilization of storage proteins such as in
seeds. In addition, they are involved
in signalling pathways and in the response
to biotic and abiotic stresses.
 http://en.wikipedia.org/wiki/Cysteine_protease

8. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 In humans and other animals, they are
responsible
for senescence and apoptosis (programmed
cell death), MHC class II immune
responses, prohormone processing,
and extracellular matrix remodeling important
to bone development.
 http://en.wikipedia.org/wiki/Cysteine_protease

9. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 The ability of macrophages and other cells to
mobilize elastolytic cysteine proteases to their
surfaces under specialized conditions may
also lead to accelerated collagen
and elastin degradation at sites
of inflammation in diseases such
as atherosclerosis and emphysema.
 http://en.wikipedia.org/wiki/Cysteine_protease

10. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.

11. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 Proteases are usually synthesized as large precursor
proteins called zymogens.
 Activation occurs once the protease is delivered to a
specific intracellular compartment (e.g. lysosome) or
extracellular environment.
 Protease inhibitors are usually proteins
with domains that enter or block a protease active
site to prevent substrate access. In competitive
inhibition, the inhibitor binds to the active site, thus
preventing enzyme-substrate interaction. In non-
competitive inhibition, the inhibitor binds to
an allosteric site, which alters the active site and
makes it inaccessible to the substrate.

12. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 . Cysteine proteases (CPs) are proteins with
molecular mass about 21–30 kDa. They show
the highest hydrolytic activity at pH 4–6.5.
Because of the high tendency of the thiol
group to oxidation, the environment of the
enzyme should contain a reducing component.
Glutathione serves as an activating agent in
cells, whereas addition of mercaptoethanol or
dithiothreitol is required for in vitro
experiments.
http://www.actabp.pl/pdf/1_2001/1-20.pdf

13. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 Structural studies of cysteine proteases and
their inhibitors. Grzonka et al.
 Mammalian cysteine proteases have been
implicated in the development and progression
of many diseases that involve abnormal
protein turnover.

14. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 Caspases, or cysteine-aspartic
proteases or cysteine-dependent aspartate-
directed proteases are a family of cysteine
proteases that play essential roles
in apoptosis (programmed cell
death), necrosis, and inflammation.
 http://en.wikipedia.org/wiki/Caspase

15. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 There are two types of apoptotic
caspases: initiator (apical)
caspases and effector (executioner) caspases.
Initiator caspases (e.g., CASP2, CASP8, CASP9,
and CASP10) cleave inactive pro-forms of effector
caspases, thereby activating them. Effector
caspases (e.g., CASP3, CASP6, CASP7) in turn
cleave other protein substrates within the cell, to
trigger the apoptotic process. The initiation of this
cascade reaction is regulated by caspase
inhibitors.
 http://en.wikipedia.org/wiki/Caspase

16. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.
 The caspase cascade can be activated by:
 granzyme B (released by cytotoxic T
lymphocytes and NK cells), which is known to
activate caspase-3 and -7
 death receptors (like Fas, TRAIL receptors
and TNF receptor), which can activate caspase-8
and -10
 the apoptosome (regulated by cytochrome c and
the Bcl-2 family), which activates caspase-9.
http://en.wikipedia.org/wiki/Caspase

17. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.

18. RADIATION TOXICITY:
HYDROLYTIC ENZYMES.