17 Ester Hydrolases, ATPases and Carboanhydrases
17.1
17.1.1
17.1.2
17.1.3
17.1.4
17.2
17.2.1
17.2.2
17.2.3
17.2.4
Carboxylester Hydrolases
Carboxyl, Aryl and Acetyl Esterases
Cholinesterases
Lipases and Cholesterol Ester Hydrolases
Phospholipases
Phosphatases and Phosphodiesterases
Alkaline Phosphatases
Acid Phosphatases
Substrate-Specific Phosphomonoesterases
cAMP and cGMP Phosphodiesterases
Many biomolecules are esterified with carbonic
acid, phosphoric acid or sulphuric acid. The enzymes responsible for the hydrolytic cleavage of the
esters are the carboxylester hydro lases , phosphoesterases and sulphatases. In addition to the
phosphomonoesterases, we will also consider the
phosphodiesterases and nucleases that are specific for cAMP and cGMP, as well as the ATPases
that cleave phosphoric acid anhydride bonds. The
ion-transporting ATPases will be discussed together with comparative biochemical data on ion
channels. The chapter ends with a discussion of
carboanhydrases.
17.1 Carboxylester Hydrolases
The carboxy lester hydrolases include the (carboxyl) esterases, lipases and cholinesterases. The
carboxylester hydrolases sequenced so far show
27-53 % sequence agreement on pairwise comparison and thus belong to the same protein
super-family. Unfortunately, the sequence data
available are insufficient to draw conclusions
about the evolution of this enzyme family and to
construct a genealogical tree. All known
carboxylester hydro lases have a serine in the active centre, but the serine esterases are not related
to the serine proteases [29, 43]. Surprisingly, the
amino acids 30-575 of acetylcholinesterase from
the electric organ of Torpedo agree about 28 %
17.2.5
17.3
17.3.1
17.3.2
17.3.3
17.3.4
17.4
17.5
Nuc1eases
ATPases (With an Excursus on Ion Channels)
Na+,K+-ATPase
Ca 2 + -ATPase
K+ ,H+ -ATPase and Anion-Sensitive ATPase
Ion Channels
Sulphatases
Carboanhydrases
References
with amino acids 2210-2750 of bovine thyroglobulin; in addition, six of the eight cysteine residues are conserved, resulting in similar folding
[146]. It is not easy to differentiate between (carboxyl) esterases and lipases. According to the
usual definition, lipases should only be active on
substrate aggregates at the ester-water interface;
in fact, lipases also cleave substrates in molecular
or micellar solution (e.g. paraoxon), whereas
microsomal carboxyl esterases also attack emulsified tributyrylglycerol. A practical distinction is
that triacylglycerols with long-chain fatty acids
are only cleaved by lipases. Amongst the enzymes
termed phospholipases some should be classified
as carboxyl esterases and others as phosphodiesterases.
17.1.1 Carboxyl, Aryl and Acetyl Esterases
The esterases cleave aliphatic esters of shortchain carboxyl acids (preferentially C3 to C6) and
also aromatic esters, aromatic amides and thioesters. Some also catalyse acyl transfer to alcohols
or amino acids. The classification of these enzymes is especially difficult for the following
reasons [123]:
1. With few exceptions, neither the natural substrate nor the biological function is known for
any esterase; artificial substrates are used for
identification and activity determinations, e.g.
17.1
17.1.1
17.1.2
17.1.3
17.1.4
17.2
17.2.1
17.2.2
17.2.3
17.2.4
Carboxylester Hydrolases
Carboxyl, Aryl and Acetyl Esterases
Cholinesterases
Lipases and Cholesterol Ester Hydrolases
Phospholipases
Phosphatases and Phosphodiesterases
Alkaline Phosphatases
Acid Phosphatases
Substrate-Specific Phosphomonoesterases
cAMP and cGMP Phosphodiesterases
Many biomolecules are esterified with carbonic
acid, phosphoric acid or sulphuric acid. The enzymes responsible for the hydrolytic cleavage of the
esters are the carboxylester hydro lases , phosphoesterases and sulphatases. In addition to the
phosphomonoesterases, we will also consider the
phosphodiesterases and nucleases that are specific for cAMP and cGMP, as well as the ATPases
that cleave phosphoric acid anhydride bonds. The
ion-transporting ATPases will be discussed together with comparative biochemical data on ion
channels. The chapter ends with a discussion of
carboanhydrases.
17.1 Carboxylester Hydrolases
The carboxy lester hydrolases include the (carboxyl) esterases, lipases and cholinesterases. The
carboxylester hydrolases sequenced so far show
27-53 % sequence agreement on pairwise comparison and thus belong to the same protein
super-family. Unfortunately, the sequence data
available are insufficient to draw conclusions
about the evolution of this enzyme family and to
construct a genealogical tree. All known
carboxylester hydro lases have a serine in the active centre, but the serine esterases are not related
to the serine proteases [29, 43]. Surprisingly, the
amino acids 30-575 of acetylcholinesterase from
the electric organ of Torpedo agree about 28 %
17.2.5
17.3
17.3.1
17.3.2
17.3.3
17.3.4
17.4
17.5
Nuc1eases
ATPases (With an Excursus on Ion Channels)
Na+,K+-ATPase
Ca 2 + -ATPase
K+ ,H+ -ATPase and Anion-Sensitive ATPase
Ion Channels
Sulphatases
Carboanhydrases
References
with amino acids 2210-2750 of bovine thyroglobulin; in addition, six of the eight cysteine residues are conserved, resulting in similar folding
[146]. It is not easy to differentiate between (carboxyl) esterases and lipases. According to the
usual definition, lipases should only be active on
substrate aggregates at the ester-water interface;
in fact, lipases also cleave substrates in molecular
or micellar solution (e.g. paraoxon), whereas
microsomal carboxyl esterases also attack emulsified tributyrylglycerol. A practical distinction is
that triacylglycerols with long-chain fatty acids
are only cleaved by lipases. Amongst the enzymes
termed phospholipases some should be classified
as carboxyl esterases and others as phosphodiesterases.
17.1.1 Carboxyl, Aryl and Acetyl Esterases
The esterases cleave aliphatic esters of shortchain carboxyl acids (preferentially C3 to C6) and
also aromatic esters, aromatic amides and thioesters. Some also catalyse acyl transfer to alcohols
or amino acids. The classification of these enzymes is especially difficult for the following
reasons [123]:
1. With few exceptions, neither the natural substrate nor the biological function is known for
any esterase; artificial substrates are used for
identification and activity determinations, e.g.