Mixed-linkage glucan : xyloglucan endotransglucosylase

Endotransglucosylase

An endotranglucosylase is an enzyme which is able to transfer a saccharide unit from one saccharide to another....

 (MXE) is a plant cell wall-modifying enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 found in plants of the Equisetum genus. The enzyme is proposed, in vivo

In vivo

In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

, to catalyse the endotransglucosylation of two different hemicellulose

Hemicellulose

A hemicellulose is any of several heteropolymers , such as arabinoxylans, present along with cellulose in almost all plant cell walls. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength...

 polysaccharides, mixed-linkage glucan

Mixed-linkage glucan

Mixed-linkage glucan , sometimes incorrectly referred to as beta-glucan, is a hemicellulosic polysaccharide consisting of β-D ad β-D linked glucosyl residues. MLG is highly prevalent within the Poales, where it has important properties in the diet...

 and xyloglucan

Xyloglucan

Xyloglucan is a hemicellulose that occurs in the primary cell wall of all vascular plants, however essential enzymes for xyloglucan metabolism, like XTH and β1→4-Glucan Synthase are found in Charophyceae algae. In many dicotyledonous plants, it is the most abundant hemicellulose in the primary cell...

, effectively 'stitching' them together. However only the 'stitching' of a mixed-linkage glucan polysaccharide to a xyloglucan oligosaccharide

Oligosaccharide

An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars...

 has actually been witnessed to date.

Location

Because the enzyme has only been assayed in a crude cell extract, the exact location of it in the plant has not been determined. However, as its two main substrates are both hemicelloses, the enzyme is expected to be found in the apoplast

Apoplast

Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant....

.

Role in planta

The precise function of MXE has yet to be elucidated, although a role in the strengthening of cell walls and thus the cessation of growth has been proposed. This is largely due to the correlation of MXE activity in crude extracts with the age of the cell, crude extracts from older cells exhibit higher MXE activity.