Translocase is a general term for a protein that assists in moving another molecule, usually across a cell membrane. These enzymes catalyze the movement of ions or molecules across membranes or their separation within membranes. The reaction is designated as a transfer from “side 1” to “side 2” because the designations “in” and “out”, which had previously been used, can be ambiguous. Translocases are the most common secretion system in Gram positive bacteria. It is also a historical term for the protein now called elongation factor G, due to its function in moving the transfer RNA (tRNA) and messenger RNA (mRNA) through the ribosome.

History

The enzyme classification and nomenclature list was first approved by the International Union of Biochemistry in 1961. Six enzyme classes had been recognized based on the type of chemical reaction catalyzed, including oxidoreductases (EC 1), transferases (EC 2), hydrolases (EC 3), lyases (EC 4), isomerases (EC 5) and ligases (EC 6). However, it became apparent that none of these could describe the important group of enzymes that catalyse the movement of ions or molecules across membranes or their separation within membranes. Several of these involve the hydrolysis of ATP and had been previously classified as ATPases (EC 3.6.3.-), although the hydrolytic reaction is not their primary function. In August 2018, the International Union of Biochemistry and Molecular Biology classified these enzymes under a new enzyme class (EC) of translocases (EC 7).

Mechanism of catalysis

The reaction most translocases catalyse is: A clear example of an enzyme that follows this scheme is H+-transporting two-sector ATPase: ATP-ADP translocase: protein responsible for the 1: 1 exchange of intramitochondrial ATP for ADP produced in the cytoplasm. B) Phosphate translocase: the transport of H2PO4- together with a proton are produced by symport H2PO4-/H+]] This ATPase carries out the dephosphorylation of ATP into ADP while it transports H+ to the other side of the membrane. However, other enzymes that also fall into this category do not follow the same reaction scheme. This is the case of ascorbate ferrireductase: In which the enzyme only transports an electron in the catalysation of an oxidoreductase reaction between a molecule and an inorganic cation located on different sides of the membrane.

Function

The basic function, as already mentioned (see: ), is to "catalyse the movement of ions or molecules across membranes or their separation within membranes". This form of membrane transport is classified under active membrane transport, an energy-requiring process of pumping molecules and ions across membranes against a concentration gradient. Translocases biological importance relies primarily on their critical function, in the way that they provide movement across the cell's membrane in many cellular processes that are substantial, such as:

Classification

The enzyme subclasses designate the types of components that are being transferred, and the sub-subclasses indicate the reaction processes that provide the driving force for the translocation. === EC 7.1 Catalysing the translocation of hydrons === This subclass contains translocases that catalyze the translocation of hydrons. Based on the reaction they are linked to, EC 7.1 can be further classified into: An important translocase contained in this group is ATP synthase, also known as EC 7.1.2.2.

EC 7.2 Catalysing the translocation of inorganic cations and their chelates

This subclass contains translocases that transfer inorganic cations (metal cations). Based on the reaction they're linked to, EC 7.2 can be further classified into: An important translocase contained in this group is Na+/K+ pump, also known as EC 7.2.2.13.

EC 7.3 Catalysing the translocation of inorganic anions

This subclass contains translocases that transfer inorganic cations anions. Subclasses are based on the reaction processes that provide the driving force for the translocation. At present only one subclass is represented: EC 7.3.2 Translocation of inorganic anions linked to the hydrolysis of a nucleoside triphosphate.

EC 7.4 Catalysing the translocation of amino acids and peptides

Subclasses are based on the reaction processes that provide the driving force for the translocation. At present there is only one subclass: EC 7.4.2 Translocation of amino acids and peptides linked to the hydrolysis of a nucleoside triphosphate.

EC 7.5 Catalysing the translocation of carbohydrates and their derivatives

EC 7.6 Catalysing the translocation of other compounds

Examples