In enzymology, a phosphatidylinositol alpha-mannosyltransferase is an 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...

 that catalyzes

Catalysis

Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....

 the chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

 in which at least one alpha-D-mannose

Mannose

Mannose is a sugar monomer of the aldohexose series of carbohydrates. Mannose is a C-2 epimer of glucose. It is not part of human metabolism, but is a component of microbial cell walls, and is therefore a target of the immune system and also of antibiotics....

 residues are transferred from GDP-mannose to positions 6, 2 and others in 1-phosphatidyl-myo-inositol

Inositol

Inositol or cyclohexane-1,2,3,4,5,6-hexol is a chemical compound with formula 6126 or 6, a sixfold alcohol of cyclohexane. It exists in nine possible stereoisomers, of which the most prominent form, widely occurring in nature, is cis-1,2,3,5-trans-4,6-cyclohexanehexol, or myo-inositol...

.

This enzyme belongs to the family of glycosyltransferase

Glycosyltransferase

Glycosyltransferases are enzymes that act as a catalyst for the transfer of a monosaccharide unit from an activated nucleotide sugar to a glycosyl acceptor molecule, usually an alcohol....

s, specifically the hexosyltransferases. The systematic name of this enzyme class is GDP-mannose:1-phosphatidyl-1D-myo-inositol alpha-D-mannosyltransferase. Other names in common use include GDP mannose-phosphatidyl-myo-inositol alpha-mannosyltransferase, GDPmannose:1-phosphatidyl-myo-inositol alpha-D-mannosyltransferase, guanosine diphosphomannose-phosphatidyl-inositol, alpha-mannosyltransferase, and phosphatidyl-myo-inositol alpha-mannosyltransferase.