In the catalytic triad

Catalytic triad

A catalytic triad refers to the three amino acid residues found inside the active site of certain protease enzymes: serine , aspartate , and histidine . They work together to break peptide bonds on polypeptides. In general terms, catalytic triad can refer to any set of three residues that function...

 of chymotrypsin, trypsin, and elastase, the three proteases function at three important molecular 'cutting' points. The sites are at amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 residues of: histidine

Histidine

Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...

 57, aspartic acid

Aspartic acid

Aspartic acid is an α-amino acid with the chemical formula HOOCCHCH2COOH. The carboxylate anion, salt, or ester of aspartic acid is known as aspartate. The L-isomer of aspartate is one of the 20 proteinogenic amino acids, i.e., the building blocks of proteins...

 102, and serine

Serine

Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...

 195.

The comparison for chymotrypsin A (cow), and trypsin (cow), and elastase (pig) is as follows:

Site: aspartic acid 102

Section showing aspartic acid

Aspartic acid

Aspartic acid is an α-amino acid with the chemical formula HOOCCHCH2COOH. The carboxylate anion, salt, or ester of aspartic acid is known as aspartate. The L-isomer of aspartate is one of the 20 proteinogenic amino acids, i.e., the building blocks of proteins...

102:

-

x	73 75 80	85	90	95	99A
C	QGSSSEKI	QKLKI	AKVFK	NSKYN	SLTI'
T	INVVEGNQ	QFISA	SKSIV	HPSYN	SNTL'
E	LNQNNGTE	QYVGV	QKIVV	HPYWN	TDDVA

- (D=Aspartic Acid 102)

x	99B 102,3,4,5	106-110	115	120	121 5,126
C	'NNDITL	LKLST	AASFS	QTVSA	VCLPSA
T	'NNDITL	IKLKS	AASLN	SRVAS	ISLPT'
E	AGYDIAL	LRLAQ	SVTLN	SYVQL	GVLPRA

-

Entire comparison of the sequences

-

x	1,2,3,4,5	6-10	15	20
C-Chymotrypsin	CGVPA	IQPVL	SGL(SR)	IVNGE
T-Trypsin	'`'`'	`'`'(V	DDDDK)	IVGGY
E-Elastase	'`'`'	`'`'`	'`'`'	VVGGT

-

x	30	35	36ABC37 40	45
C	EAPVG	SWPWQ	DK'`'TGTH	FCGGS
T	TCGAN	TVPYQ	'`'`'SGYH	FCGGS
E	EAQRN	SWPSQ	ISLQYRSGSWAH	TCGGT

-
Section showing histidine 57:
-

x	46-50	55	56,57-60	65	65A 66-70
C	LINEN	WVVTA	AHCGV	TTSDV	'VVAGEFD
T	LINSQ	WVVSA	AHCYK	SGIQV	RL'`GQDN
E	LIRQN	WVMTA	AHCVD	RELTF	RVVVGEHN

-

x	73-75-80	85	90	95	96-99A
C	QGSSSEKI	QKLKI	AKVFK	NSKYN	SLTI'
T	INVVEGNQ	QFISA	SKSIV	HPSYN	SNTL'
E	LNQNNGTE	QYVGV	QKIVV	HPYWN	TDDVA

-

x	99B 102,3,4,5	106-110	115	120	121 5,126
C	'NNDITL	LKLST	AASFS	QTVSA	VCLPSA
T	'NNDITL	IKLKS	AASLN	SRVAS	ISLPT'
E	AGYDIAL	LRLAQ	SVTLN	SYVQL	GVLPRA

-

Remaining half of the sequence, 127-245, not shown. (site serine 195, not shown)