Binding Specificity (PH 01-06)

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BY: PHARMACEUT

BINDING SPECIFICITY


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INTRODUCTION

Enzymes are globular proteins. Their folded conformati

area known as the ac!"# $!#. The nature and arrangemacids in the active site make it specic for only one type of
http://www.phschool.com/science/biology_place/glossary/a.htmlhttp://www.phschool.com/science/biology_place/glossary/a.html


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Chemically specicity is the ability of a protein binding

specic ligandsThe fewer ligands a protein can bind , the greater its s

Even when dierent substrate molecules are present, othat have the specic shape complementary to the actable to bind with the enzymes active site.


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CONCEPT

!pecicity refers to both $%#c!&c!' () *!+,!+ a+,

() #ac!(+.Certain active site constituents are involved in these b

characteristics which are responsible for binding speci

B!+,!+ S%#c!&c!' :

"a#imum binding interactions at active site occurs attransition state of the reaction. Enzyme binds transitioabout $%$&times more tightly than it binds to the subsproduct.


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't is important that the enzyme does not bind to interm

states e#cessively or this will increase the free energy dbetween the intermediate and the transition state.

(inding specicity can be absolute, that is ,essentially osubstrate forms an E.! comple# with a particular enzymthen leads to product formation.

!pecicity may involve E.! comple# formation with onlyenantiomer of a racemate or E.! comple# formation witenantiomer ,but only one is converted to product.


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REACTION / EAMPLE

The reason for specicity of the binding is that en

itself a chiralmolecule )mamalian enzymes are comprised of

amino acids.

Therefore interaction of enzyme with racemic mi#results in formation of & diastereomeric comple#e


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RESOLUTION OF RACEMIC MITURES ITH CHIRAL R

R3-24#'*#+'7a4!+#

Chiralreagent

/iasteromeric salts ) no longer enatiomers can beseparated by physical means


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BINDING OF THE SUBSTRATE ITH AN EN8YME0hen an enzyme is e#posed to racemi# mi#ture of a substrate, the binding energy for E+! comple# formation with one enatiomer may be much highenatiomer because of the dierential binding interaction or stearic reasons.eg. phenylalanine )benzyl group has & possible orientations )! )-

(inding pocketfor )! isomer

!tearic hindrancewith )- isomer

Ac!"# $!#() ##+'4#

L#9c!+# $!,# ca!+

D!##+!a7 *!+,!+ !+#ac!(+$ *' #+a+!(4#$

F(4a!(+ ()(,9c

N(+ %(,9c!"#*!+,!+


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TYPES OF BINDING SPECIFIC


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Enzyme specic to only one substrate and one reac

!pecicity is high.1lso called as substrate specicity.'t is the ability of an enzyme to choose e#act subst

Eg2 $+*actase acts only on lactose to form 3lucose 3alactose.

&+"altase acts only on "altose to give & molecu3lucose.

C$&4&&5$$)16 7 4&5 )l +8 & C94$&59)16

"altose 3lucose

ABSOLUTE SPECIFICITY


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T# #+'4#$ ;!77 ac (+7' (+ 4(a a"# $%#c!&c)9+c!(+a7(9%.

T# #+'4#$ $%#c!&c (9%$$9(

! ( ( '%#()*(+,.

GROUP SPECIFICITY


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Example2 P#%$!+hydrolyze a peptide bond in which amis contributed by a(4a!c a4!+( ac!,$. ):henylalanin

Tryptophan.


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%#%!,a$# H',(7'#$ # P#%!,# B(+, F(4 N-#


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P(#(7'!c #+'4#$show linkage specicity.4ydroyse specic bonds with a specic side chain grou

:roteolytic enzymes2 Enzymes involved in hydrolysing pbond

E


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LIN=AGE SPECIFICITY


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!ilverman Enzyme Chapter :g $9>en.wikipedia.org>wiki>B!+,!+?sey

REFERENCE


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THAN= YOU

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Binding Specificity (PH 01-06)