1

Metabolism of protein &

amino acids

2

A. The physiological &

nutritious function of

proteins

3

B. nitrogen balance &

protein requirement

4

1. nitrogen balance

a. concept

b. experiment

5

c. 3 conditions

nitrogen equilibrium

negative nitrogen balance

positive nitrogen balance

6

2. minimal requirements of

protein

3.essential amino acids and

their biological value

7

8

an indicator to valuate the

nutritional value of the proteins

biological value

100 的吸收量的保留值

蛋白质的生理价值＝N

N

9

4. Complementary function

of proteins

B. Digestion ,absorption,&

putrefaction of proteins

10

diet protein amino acids digestion

Proteolytic

enzyme

a. digestion

11

b. absorption

site

mechanism

characteristics

12

14

c. putrefaction

concept

15

未被消化的蛋白质 , 未被吸收的氨基酸，肽

large intestine

bacterias

Decarboxylation

deamination

有毒； amine ,H2S indole

hydroxybenzene 、 ammonia （ NH3) 、

other ：CO2,CH4

Nutriment

Fatty acid 、 vit

Absorption in intestine excrete

blood

liver

16

• decarboxylation

• reductive & deamination

17

18

19

• the sources of ammonia in the

intestine

20

blood infiltrate intestine

kidney

excrete （ 20g ）

NH2-CO-NH2

liver

NH3

(25%)7g

NH2-CO-

NH2

urease (bacterias)

2NH3+CO2 （ 4g

）

importance sources of blood ammonia-----

- absorpted from intestine

21

C. general metabolism

of amino acids

1. Sketch plan

23

Dietary protein

Tissue protein

amination of α—keto acids

degradation

Synthesis

85%

Non essential A.A

Digest,absorption

deamination

amines

NH3 α—keto acids

oxidation Glucose, fats

N.EAA

decarboxylation

Amino acid

metabolic

pool

urea

other substances

24

2. deamination of amino acids

a.oxidative deamination

1) reaction

25

26

2 ) enzymes

• L-amino acid oxidase

• D-amino acid oxidase

• L-glutamate dehydrogenase

27

28

• characteristics

b . transamination

1) reaction

29

30

2) important transamination

system.

31

glutamic pyruvic transamination system （ glutamic pyruvic transaminase,GPT ）（ alanine transaminase,ALT ）

glutamic oxaloacetic transamination systen: （ glutamic oxaloacetic transaminase, ,GOT ）（ aspartate transaminase,AST)

32

NH2 O O NH2

Glu 丙酮酸 α— 酮戊二酸 Ala

NH2 CO-COOH O CH-COOH

NH2

Glu 草酰乙酸 α— 酮戊二酸 ASP

COOH-(CH2)2-CH-COOH + CH3-C-COOH COOH-(CH2)2-C-COOH+CH3-CH-COOH

COOH-(CH2)2-CH-COOH + CH2COOH COOH-(CH2)2-C-COOH+CH2-COOH

ALT

AST

33

2) enzyme & coenzyme

35

36

3) biological significance &

characteristics

37

c. combined deamination

1) reaction

38

39

40

41

2) biological significance &

characteristics

42

d. purine nucleotide cycle

1) site

2) reaction

43

44

3) characteristics

45

d. nonoxidative deamination

• dehydrate deamination

• direct deamination

46

47

3. Metabolism of ammonia

a. the sources of ammonia

48

the detail about the sources

of ammonia

49

protein

putrefaction

Urea cycle in liver&intestine

Absorption in intestine

（ oxidation of amine )

　 deamination

Blood ammonia

Ala

(liver)

Gln

  sources of blood ammonia

50

* protein putrefaction

51

blood infiltrate intestine

kidney

excrete （ 20g ）

NH2-CO-NH2

liver

NH3

(25%)7g

NH2-CO-

NH2

urease

2NH3+CO2 （ 4g

）

importance sources of blood ammonia-----

- absorpted from intestine

NH4 excrete from feces

*Urea cycle in liver & intestine

52

According to the pH in intestine

pH NH3 + H+ NH 4+ excrete

  pH absorpted to venous blood

53

protein

putrefaction

Urea cycle in liver&intestine

Absorption in intestine

（ oxidation of amine )

　 deamination

Blood ammonia

Ala

(liver)

Gln

  sources of blood ammonia

54

* hydrolysis of Gln

55

• the fates of ammonia

produced in renal cell

excrete to the kidney

reabsorption to vein blood

56

According to renal tube pH

pH NH3 + H+ NH4+ excrete

 pH absorpted to venous blood

57

Putrefaction in

small intestine

Intestine-liver

cycle of urea

Absorption

In small intestine

（ oxidation of amines ）

deamination of A.A

Ammonia

in blood

Ala in liver

GLn

58

*Ala

59

b. The transportation of

ammonia

• synthesis & utilize of Gln

materials : Glu , NH3

60

energy: ATP

enzyme: Gln synthetase

reaction:

61

62

product: Gln

Biological significances

,

63

• glucose-alanine cycle

process

64

65

biological significance

66

Putrefaction in

small intestine

Intestine-liver

cycle of urea

Absorption

In small intestine

（ oxidation of amines ）

deamination of A.A

Ammonia

in blood

Ala in liver

GLn

67

c. the fates of ammonia

68

Synthesis of non essential A.A or other nitrogen compounds

muscle or other tissues

Gln

muscle

ureaNH3

Ala

liver

69

1) synthesis of urea---main

outlet of ammonia

a. site

b. process (ornithine cycle )

70

* 肝脏是合成尿素最主要的器官

血 尿

切肝犬 尿素 氨 尿素

用氨基酸饲养切肝犬 尿素 氨基酸

尿素 切肾犬

急性黄色肝委缩

氨基酸

尿素 （ - ） 氨 尿素 （ - ）

72

73

This cycle included:

1 overall reaction

2 materials

3 stages

4 steps

5 enzymes

74

a. materials

15NH4Cl

NaH14CO3

Feed

dogs

14C=O

15NH2

15NH2

75

b. 3 stages

ornithine+ NH3+ CO2 citrulline+H20

citrulline+ NH3 arginine+ H20

arginine+ H20 urea+ ornithine

2ATP

1ATP

77

NH2 NH2

(CH2)3 C=O

+ NH3+ CO2 NH + H2O

CH NH2

(CH2)3

CH NH2 ornithine

citrulline

COOH

COOH

2ATP

78

NH2 NH2

C=O

NH + NH3 NH + H2O

(CH2)3

CH-NH2

COOH Citrullinc Arginine

C=NH

(CH2)3

CH-NH2

COOH

1ATP

79

NH2

C=NH

NH +H2O

(CH2)3

CH-NH2

COOH

Arginine

NH2 + (CH2)3

C=O CH-NH2

Orrnithine

COOH

NH2

NH2

urea

80

NH3 （ 2 molecules ）

CO2 （ 1 molecules ） materials

urea

H2O

products

Ornithine

Citrulline

arginine

intermediates

81

c. Intermediate process

( 4 steps, 5 enzymes )

1) synthesis of carbomoyl

phosphate (mitochondria)

82

83

NH3+CO2+H2O+2ATP

NH2-CO-O~PO32-+Pi

carbomoyl phosphate synthetase 1

84

• enzyme

carbamoyl phosphate synthetase 1 carbamoyl phosphate synthetase II

85

carbomoyl phosphate carbomoyl phosphate

synthetase 1 synthetase II

Site mitochondria cytosol

source of NH3 Gln

nitrogenActivator AGA -

(N-Acetylglutamic acid )FinalProduct urea pyrimidine

86

2) synthesis of citrulline

(mitochondria)

• enzyme

ornithine transcarbomoylase

87

88

3) synthesis of arginine

(cytosol)

• enzyme

Argininosuccinate synthetase,ASAS Argininosuccinate lyase ASAL

ASAS------ Key enzyme

89

90

4) cleavage of arginine

(cytosol)

91

93

94

d. Overall reaction

3ATP+CO2+2NH3 +H2O NH2-CO-NH2

f. summarize

95

c. Regulation of urea synthesis

food

enzymes (AGA)

intermediates

96

97

d. biological significant of

urea synthesis

98

Synthesis of non essential A.A or other nitrogen compounds

muscle or other tissues

Gln

muscle

ureaNH3

Ala

liver

99

4. Metabolism of -keto acids

Amino

acid

NH3

Ala

Gln

ureaAmination of a-keto acids

Amination or transamination

To form non E.A.A.

Conversion of fat,glucose

Via TCA cycle oxidized to CO2 & H2O

-keto acids

100

1) Amination or transamination

To form non E.A.A.

α- ketoglutarate Glu

Pyruvate Ala oxaloacetate Asp

101

Glu

α- ketoglutarate

oxaloacetate

Asp

TCA cycle

102

2) Conversion to lipids or

carbohydrates

glycogenic amino acid, such as : Ala 、 Arg 、 Asp etc （ 13 ）ketogenic amino acid such as:

leu lys (2)

glycogenic & ketogenic amino

acids such as : Ilu,Phe,Trp,Tye

103

TCA cycle is the hinge

of metabolism of lipids ,

carbohydrates, proteins

104

*

*

*

*

*

*

*

*

105

3) oxidation & provide energy

3. decarboxylation

106

Amino acids - CO

2

α-keto acids

amines

Non E.A.A

Conversion to lipids, carbohydrates

TCA cycle- NH 3

107

Enzymes & coenzyme

some important amines

108

a.γ-amino butyric acid

(GABA ）

formation

109

enzyme

function

metabolic fate

110

b. 5-hydroxy tryptamine or

( serotonin ）formation

111

function

c. taurine

formation

112

function

d. histamine

formation

113

e. polyamines

formation

114

115

D. metabolism of individual

amino acids

1. one carbon units

116

Concept

kinds

117

118

the carrier of one carbon unites

--------------THF

120

the sources & conversion

NH2-CH——COOH +FH4 NH2-CH— （ CH2 ） 2+N5-CH3-FH4 转甲基酶

（ CH2 ）

2

S

CH3

SH COOH

121

122

123

function

one carbon units &

medicine

124

2. metabolism of sulfur-

containing amono acids

types

125

Met

cysteine,Cys cystine

126

a.Met and Transfer of

methyl group

S-adenosylmethionine

(SAM)

127

Structure of SAM

128

Function of SAM

methionine cycle

B12 & methionine

cycle

129

B12

130

3. metabolism of cystein &

cystine

structure & characteristics

131

Formation of GSH

132

Catabolism of Cys

Cys

-NH2

pyruvate NH3 H2S

H2S SO42- 2ATP

Excrete in uria PAPS （ active sulfate ）

133

The structure & function

of PAPS

( 3’-phosphoadenosine-

5’phosphosulfate

134

135

4. metabolism of side

chain amino acids

Type: Val,Ile,Leu

Catabolic process

(extrahepatic tissue )

136

Val 、 Ile 、 Leu

α-ketoacids

α-ketoglutarate Glu NH3

Gln

Ala pyruvate

liver

urea glyconeogenesis

Blood

137

5. metabolism of

aromatic amino acids

Type: Phe,Tyr,Trp

Catabolic process

(hepatic tissue)

138

Catabolic process of Phe

139

140

Albinism,

Phenylketonuria, (PKU)

Alkaptonuria

BCAA/AAA 3:1