In the field of
enzymology
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
, a proton ATPase, or H
+-ATPase, is an
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
that
catalyzes
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
the following
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
:
:ATP + +
in ADP + phosphate +
out
The 3
substrates of this enzyme are
ATP, , and , whereas its 3
products
Product may refer to:
Business
* Product (business), an item that can be offered to a market to satisfy the desire or need of a customer.
* Product (project management), a deliverable or set of deliverables that contribute to a business solution
...
are
ADP,
phosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
, and .
Proton ATPases are divided into three groups
as outlined below:
P-type proton ATPase
P-type ATPase
The P-type ATPases, also known as E1-E2 ATPases, are a large group of evolutionarily related ion and lipid pumps that are found in bacteria, archaea, and eukaryotes. P-type ATPases are α-helical bundle primary transporters named based upon thei ...
s form a covalent phosphorylated (hence the symbol ’P') intermediate as part of its reaction cycle. P-type ATPases undergo major conformational changes during the catalytic cycle. P-type ATPases are not evolutionary related to V- and F-type ATPases.
Plasma membrane H+-ATPase
P-type proton ATPase (or
plasma membrane -ATPase) is found in the plasma membranes of eubacteria, archaea, protozoa, fungi and plants. Here it serves as a functional equivalent to the
Na+/K+ ATPase of animal cells; i.e. it energizes the plasma membrane by forming an electrochemical gradient of protons (Na
+ in animal cells), that in turn drives secondary active transport processes across the membrane. The plasma membrane H
+-ATPase is a
P3A ATPase with a single polypeptide of 70-100 kDa.
Gastric H+/K+ ATPase
Animals have a gastric
hydrogen potassium ATPase
Gastric hydrogen potassium ATPase, also known as H+/K+ ATPase, is an enzyme which functions to acidify the stomach. It is a member of the P-type ATPases, also known as E1-E2 ATPases due to its two states.
Biological function and location
The ...
or H
+/K
+ ATPase that belongs to the P-type ATPase family and functions as an electroneutral proton pump. This pump is found in the plasma membrane of cells in the
gastric mucosa
The gastric mucosa is the mucous membrane layer of the stomach, which contains the gastric pits, to which the gastric glands empty. In humans, it is about one mm thick, and its surface is smooth, soft, and velvety. It consists of simple secretor ...
and functions to acidify the stomach. This enzyme is a
P2C ATPase, characterized by having a supporting beta-subunit, and is closely related to the
Na+/K+ ATPase.
V-type proton ATPase
V-type proton ATPase (or
V-ATPase) translocate protons into intracellular organelles other than mitochondria and chloroplasts, but in certain cell types they are also found in the plasma membrane. V-type ATPases acidify the lumen of the vacuole (hence the symbol 'V') of fungi and plants, and that of the lysosome in animal cells. Furthermore, they are found in endosomes, clathrin coated vesicles, hormone storage granules, secretory granules, Golgi vesicles and in the plasma membrane of a variety of animal cells. Like F-type ATPases, V-type ATPases are composed of multiple subunits and carry out rotary catalysis. The reaction cycle involves tight binding of ATP but proceeds without formation of a covalent phosphorylated intermediate. V-type ATPases are evolutionary related to F-type ATPases.
F-type proton ATPase
F-type proton ATPase (or
F-ATPase) typically operates as an ATP synthase that dissipates a proton gradient rather than generating one; i.e. protons flow in the reverse direction compared to V-type ATPases. In eubacteria, F-type ATPases are found in plasma membranes. In eukaryotes, they are found in the mitochondrial inner membranes and in chloroplast thylakoid membranes. Like V-type ATPases, F-type ATPases are composed of multiple subunits and carry out rotary catalysis. The reaction cycle involves tight binding of ATP but proceeds without formation of a covalent phosphorylated intermediate. F-type ATPases are evolutionary related to V-type ATPases.
References
{{DEFAULTSORT:Proton Atpase
Transmembrane proteins