kuliah protein bms 2 2014-2015 fkuy

8/10/2019 Kuliah Protein BMS 2 2014-2015 FKUY

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Protein

Harliansyah, Ph.D

Bagian Biokimia FK Univ YARSI

2014


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Naming of Peptides

For naming peptides, the AA suffixesine(glycine), - an (tryptophan) ate (glutamate) arechanged toyl with the exception of C

terminal AA.

A tripeptide composed of an N

terminalglutamate, a cysteine and a Cterminalglycine is called:

glutamylcysteinyl - glycine


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Function of proteins

Proteins

are the most

important buffers in

the body.

Enzymatic catalysis

Transport and storage (the protein hemoglobin,

albumins)

Coordinated motion (actin and myosin).

Mechanical support(collagen).

Immune protection(antibodies)

Generation and transmission of nerve impulses

- some amino acids act as neurotransmitters,

receptors for neurotransmitters, drugs, etc. are

protein in nature. (the acetylcholine receptor),

Control of growth and differentiation-

transcription factors

Hormones

growth factors ( insulin or thyroid stimulating

hormone)

Why?

(a) Protein moleculespossess basic and

acidic groups which act

as H+ acceptors or

donors respectively if

H+ is added or removed.


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Peptides of Physiologic Importance

1. Glutamine (Glutathione)

- a tripeptide composed

of 3 AA

- gamma

glutamyl

cysteinyl glycine

- wildly distributed in

nature

- exists in reduced or

oxidized states


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Functions:

a) As a coenzyme for certain enzymes as

prostaglandin PGE2 synthase

glycoxylase

b) Prevents the oxidation of sulfhydryl groups of several proteins

to disulfide groupsc) In association with glutathione reductase participates in the

formation of correct disulfide bonds in several protiens

d) In erythrocytes

- maintains RBC membrane structure and

integrity- protects hemoglobin from getting oxidized by agents

such as H2O2


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e) Involved in the transport of AA in theintestine and kidney tubules via delta

glutamyl cycle or Meister cycle

f) Involved in the detoxification process

g) Toxic amounts of peroxidases and free

radicals produced in the cells arescavanged by glutathione peroxidase ( aselenium containing enzyme).


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2. Thyrotropin Releasing Hormone (TRH)

- a tripeptide secreted by hypothalamus

Function:

Stimulate pituitary gland to release thyrotropic hormone

3. Oxytocin

- contains 9 AA (nonapeptide)

- hormone secreted by posteriorpituitary gland

Function:

Stimulate contraction of the uterus muscle duringdelivery

Stimulate contraction of muscle in breasts for milkejection


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- they differ in their

physicochemical properties

which ultimately determine

the characteristics of proteins


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HemoglobinStructure

HemeCenter is Iron (4 per molecule

Iron binds to the oxygen1 per Iron

250 million Hb per cell


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Hemoglobin Properties At the tertiary level, the surface residues of the aand b

subunits form complementary sites that promote tetramer

formation (a2b2), the normal physiological form ofhemoglobin.

Contains 4 heme groups, so up to 4 O2can be bound

Its physiological role is as a carrier/transporter of oxygen fromthe lungs to the rest of the body, therefore its oxygen bindingaffinity is much lower than that of myoglobin.

If the Fe2+ becomes oxidized to Fe3+ by chemicals oroxidants, oxygen can no longer bind, called Methemoglobin

kuliah protein bms 2 2014-2015 fkuy

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