Myoglobin by KK Sahu sir

INTRODUCTION
DISCOVREY OF MYOGLOBIN STRUCTURE
STRUCTURE OF MYOGLOBIN
APOMYOGLOBIN
MECHANISM-
BINDING OF OXYGEN TO MYGLOBIN
DISASSOCIATION OF OXYGEN FOROM MYOGLOBIN
IMPORTANT FEATURES OF MYOGLOBIN
BIOLOGICAL SIGNIFICANCES OF MYOGLOBIN
CONCLUSION
REFERENCES

1. MYOGLOBIN
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. SYNOPSIS--
INTRODUCTION
DISCOVREY OF MYOGLOBIN STRUCTURE
STRUCTURE OF MYOGLOBIN
APOMYOGLOBIN
MECHANISM-
BINDING OF OXYGEN TO MYGLOBIN
DISASSOCIATION OF OXYGEN FOROM MYOGLOBIN
IMPORTANT FEATURES OF MYOGLOBIN
BIOLOGICAL SIGNIFICANCES OF MYOGLOBIN
CONCLUSION
REFERENCES

3. INTRODUCTION
Myoglobin word is derived from two Gr. word
MYO-MUSCLEand GLOBIN-AKINDOF
PROTEIN.
Myoglobin is a globular protein, having
tertiary structure.
Myoglobin is a oxygenbindingprotein
present in large multicellular organisms and
stores the oxygen in muscles.

4. DISCOVERY OF MYOGLOBIN STRUCTURE
The first x-ray studies were carried out by
J.C.KENDREWand his colleagues in
England of spermwhalemyoglobin.
The x-ray diffraction pattern of crystalline
myoglobin ,which contain about 25,00 atom
;consists of nearly 25,000 reflection.

5. Analysis of structure of myoglobin took place
in two stages—
[A] Infirststage-in 1957 the results were
calculated to 0.6 nm resolution,a feat that
required precise analysis of 400 of diffraction
spots.
This degree of resolution was insufficient to
reveal the exact position of individual atoms.

6. The first step did indicate how the
polypeptide chain backbone is folded in the
myoglobin molecule.
[B] Insecondstage—The x-ray analysis of
myoglobin was carried out to 0.2nm
resolution required the analysis of some
10,000 reflection.
High sepeed electronic computting were
used.

7. This level of resolution was sufficiently high
to identify the sequence of most of the R
groups, which agreed with the amino acid
sequence determined by chemical methods.
The backbone of myoglobin molecule consist
of eight relatively straight segments set off by
bends.

8. Although the three dimensional structure of
myoglobin appears irregular and asymmetric,
it is not at all random.
All myoglobin molecule have the same
confermation , otherwise myoglobin could not
crystallize and yield reproducible x-ray
diffration patterns.

9. FIG—
MYOGLOBIN
CRYSTALS
AND X-RAY
DIFFRACTION
OF
MYOGLOBIN

10. STRUCTURE OF MYOGLOBIN
Myoglobin is a single polypeptide chain 153
amino acid residues with one molecule of
heme.
Myoglobin consists of eight helices linked by
short polypeptide segments to form an
ellipsoidal molecule of approximate
dimension 45×35×25 (in angustram).

11. A notable feature of whole myoglobin is that
the absence of disulphide bridge , since both
cystine and cysteine residuces are lacking.
Myoglobin contain only a single polypeptide
chain and one oxygen binding site.
The molecule is very compact and leaves
very little space in it’s interior.

13. 3 DIMENTIONAL STRUCTURE OF MYOGLOBIN

14. Fig---Helix F with heme molecule

15. APOMYOGLOBIN
Myoglobin without it’s heme prosthetic group
dasignated as apomyoglobin .
The main function of apomyoglobin molecule
is to provide a hydrophobic environment for
the heme group and a properly oriented
imidazol group to occupy the 5th
coordination position of the iron.

16. The presence of the hydrophobic histidin
enable the heme to combine reversibly with
oxygen and prevent the oxidation of ferrous
to ferric.

17. MECHANISM
Myoglobin plays two main functions---
1.Binding of oxygen,
2.Disassociation of oxygen.

18. 1.BINDING OF OXYGEN TO MYOGLOBIN
One globin subunit of myoglobin contain a heme
prosthetic group.
Heme is a protoporphyrin IXwith an iron atom in
it’s centre.
The iron is in the ferrous state in functional
myoglobin, where it can form five or six covalent
bond depending on whether or not oxygen is bond
to it.

19. Four bond are to the pyrrole nitrogen atom of
the porphyrin.
The heme is positioned within a hydrophobic
pocket of each globin subunit with
approximatly 80 interaction provided by
about 18 residues mostly between apolar
side chain and the apolar region of the
porphyrin.

20. The driving force for these interactions is the
expulsion of water of solvation on association
of the hydrophobic heme with the apolar side
chains in the heme pocket.
Aaddition interactions in myoglobin are
made between the negative charged
propionate groups of the heme and positively
harged arginine and histidine side chain.

21. A HEME MOLECULE
A HEME MOLECULE

22. BINDING OF
OXYGEN TO
HEME OF
MYOGLOBIN

23. FIG-GRAPH FOR OXYGEN BINDING

24. 2.DISASSOCIATION OF OXYGEN
Myoglobin binds and releases oxygen with
change in oxygen concentration in the
sarcoplasm of skeletal muscle cell.
The bjnding of oxygen to apparent from the
oxygen disassociation curve for the
myoglobin isHYPERBOLIC.

25. Fig-Oxygen
disassociation
Curve for
myoglobin

26. From the oxygen disassociation curve it can
also be seen that for any perticular oxygen
pressure the degree of saturation is high.
The binding of oxygen to the single
polypeptide unit of myoglobin is NON
COOPERATIVE.

28. IMPORTANT FEATURES OF MYOGLOBIN
The myoglobin is very compact ,in it’s interior
there is only room for four molecule of water.
All the polar hydrophobic R groups of the
amino acid residues are located on the outer
surface of the molecule and are hydrated.

29. Nearly all the nonpolar or hydrophobic R
group are in the interior of the molecule
hidden from exposure to water.
Proline residuce occure only at the bands ,
which also contain some amino acid known
not to form α helical coils readily, such as
isoleucin, serine, threonine and asparagine.

30. The gross confermation of the polypeptide
chain is apparently in myoglobins of all
species examined although they differ
somewhat in amino acid composition, thus
the conserved or invariant residues the
position of the bends and directions of the
straight segment.

31. The interior consists almost
entirely of nonpolarresiduces
such as Leu, Val, Met, Phe;onthe
contrary Glu, Asp, Gln,Argare
from the interior of the protein.
Residuceswith polar and
nonpolarparts within them [thr,
tyr] are so oriented that their
nonpolarportiospoint inward.

32. The only polar residuces inside
myoglobin are two histidines which
have a critical function at the
binding site .The exterior of the
protein has both polar and nonpolar
residues.

33. BIOLOGICAL SIGNIFICANCE OF MYOGLOBIN
Myoglobinis found in skeletal muscle
cells and is perticularlyabundant in
diving mammals like the whale, seal
and walrus , whose muscles are so rich
in myoglobinthat they are DEEP
BROWN .
Myoglobinnot only stores oxygen but
also enhance it’s rate of diffusion
through the cell.

34. Myoglobin is a model for what
occurs when a single protomer
molecule acts alone without the
interactions exhibited among the
four oxygen binding site in the more
complex tetramer molecule of
hemoglobin.

35. Muscles myoglobin permit storage
and distribution of oxygen to the
diving animals to remain
submerged for long periods of
times.

36. COCLUSION
Due to it’s specific structure
myoglobin plays an Important role
in oxygen storage.
myoglobin facilitate oxygen
diffusion in rapidly contracting
muscle tissues.

37. Nelson and Cox
B.D..Hamer and N.H.
Hooper
Devlin
Lehninger
•Principle of
biochemistry
•Biochemistry
•Biochemistry—
•Text of book
Biochemistry—
•www.elp.manchester
.c.uk/..../htm
NAMEOF THE BOOK AURTHER
1.Text book on biochemistry 2
nd
edition
Lehninger
2.Principle ofbiochemistry Nelsionand Cox
3.Biochemistry Devlin
4.Biochemistry
5.www.wiclepidia.org
6.www.elp.manchaster.c.uk/…../htm
B.D.Hamerand N.H. Hooper