This document discusses the chemical properties of proteins. It begins with an introduction to proteins and their composition of amino acids. Then it outlines several specific chemical properties of proteins, including that they can be hydrolyzed by acidic or alkaline agents into amino acids. It also describes reactions involving the carboxyl group and specific amino acid residues such as arginine, glutamic acid, aspartic acid, cystine, and cysteine. Reactions include salt formation, esterification, derivatives with dicarbonyl compounds, and alkylation.

1. CHEMICAL
PROPERTIES OF
PROTEIN
BY SADDAM HUSSEIN

2. CONTENTS
INTRODUCTION
PROTIENS
CHEMICAL PROPERTIES OF
PROTEINS

3. INTRODUCTION
SADDAM HUSSEIN
BS FOOD SCIENCE AND TECHNOLOGY
MINHAJ UNIVERSITY, LAHORE

4. PROTEINS
 Proteins are large, complex
molecules that play many critical
roles in the body.
 Proteins are made up of hundreds
or thousands of smaller units called
amino acids, which are attached to
one another in long chains.
 Proteins are classified on the base
of Structure

5. CHEMICAL PROPERTIES OF PROTEINS
Hydrolysis
Reactions involving COOH Group
Arginine Residue
Glutamic and Aspartic Acid Residues
Hydrolysis

6. CONTI…
Cystine Residue
Cysteine Residue

7. HYDROLYSIS
o Proteins are hydrolyzed by a variety of
hydrolytic agents.
o By acidic agents: Proteins, upon
hydrolysis with conc. HCl (6–12N) at 100–
110°C for 6 to 20 hrs, yield amino acids in
the form of their hydrochlorides.
o By alkaline agents: Proteins may also be
hydrolyzed with 2N NaOH.

8. REACTIONS INVOLVING COOH GROUP
o Reaction with alkalies (Salt
formation)
o Reaction with alcohols
(Esterification)
o Reaction with amines

9. ARGININE RESIDUE
o The arginine residue of proteins reacts with α-
or β-dicarbonyl compounds to form cyclic
derivatives.
o The nitropyrimidine derivative absorbs at 335
nm.
o The arginyl bond of this derivative is not
cleaved by trypsin but it is cleaved in its
tetrahydro form, obtained by reduction with
NaBH4.
o In the reaction with benzil, an
iminoimidazolidone derivative is obtained after
a benzilic acid rearrangement.

10. GLUTAMIC AND ASPARTIC ACID RESIDUES
o These amino acid residues are usually esterified
with methanolic HCl.
o There can be side reactions, such as
methanolysis of amide derivatives or N,O-acyl
migration in serine or threonine residues
o -Diazoacetamide reacts with a carboxyl group
and also with the cysteine residue
o Amino acid esters or other similar nucleophilic
compounds can be attached to a carboxyl group
of a protein with the help of carbodiimide

11. CYSTINE RESIDUE
o Cleavage of cystine is possible by a nucleophilic attack:
o The nucleophilic reactivity of the reagents decreases in the series:
hydride> phosphite> alkanethiol > aminoalkanethiol> thiophenol
and cyanide> sulfite> OH−> p-nitrophenol> thiosulfate >
thiocyanate. -Complete cleavage with sulfite requires that oxidative
agents (Cu2+) be present and that the pH be higher than 7:

12. CYSTEINE RESIDUE
o A number of alkylating agents yield derivatives
which are stable under the conditions for acidic
hydrolysis of proteins.
o The reaction with ethylene imine giving an S-
aminoethyl derivative and, hence, an additional
linkage position in the protein for hydrolysis by
trypsin.
o Iodoacetic acid, depending on the pH, can react
with cysteine, methionine, lysine and histidine
residues