Numeral prefix

Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and other European languages, they are used to coin numerous series of words, such as unicycle – bicycle – tricycle, dyad – triad – decade, biped – quadruped, September – October – November – December, decimal – hexadecimal, sexagenarian – octogenarian, centipede – millipede, etc. There are two principal systems, taken from Latin and Greek, each with several subsystems; in addition, Sanskrit occupies a marginal position. There is also an international set of metric prefixes, which are used in the metric system, and which for the most part are either distorted from the forms below or not based on actual number words.

Table of number prefixes in English

In the following prefixes, a final vowel is normally dropped before a root that begins with a vowel, with the exceptions of bi-, which is bis- before a vowel, and of the other monosyllables, du-, di-, dvi-, tri-, which are invariable.

HEXA

Hexosaminidase A (alpha polypeptide), also known as HEXA, is an enzyme that in humans is encoded by the HEXA gene, located on the 15th chromosome.

Hexosaminidase A and the cofactor G_M2 activator protein catalyze the degradation of the G_M2gangliosides and other molecules containing terminal N-acetyl hexosamines. Hexosaminidase A is a heterodimer composed of an alpha subunit (this protein) and a beta subunit. The alpha subunit polypeptide is encoded by the HEXA gene while the beta subunit is encoded by the HEXB gene. Gene mutations in the gene encoding the beta subunit (HEXB) often result in Sandhoff disease; whereas, mutations in the gene encoding the alpha subunit (HEXA, this gene) decrease the hydrolysis of G_M2 gangliosides, which is the main cause of Tay–Sachs disease.

Function

Even though the alpha and beta subunits of hexosaminidase A can both cleave GalNAc residues, only the alpha subunit is able to hydrolyze G_M2 gangliosides. The alpha subunit contains a key residue, Arg-424, which is essential for binding the N-acetyl-neuramanic residue of G_M2 gangliosides. The alpha subunit can hydrolyze G_M2 gangliosides because it contains a loop structure consisting of the amino acids: Gly-280, Ser-281, Glu-282, and Pro-283. The loop is absent in the beta subunit, but it serves as an ideal structure for the binding of the G_M2 activator protein (G_M2AP) in the alpha subunit. A combination of Arg-424 and the amino acids that cause the formation of the loop allow the alpha subunit to hydrolyze G_M2 gangliosides into G_M3 gangliosides by removing the N-acetylgalactosamine (GalNAc) residue from G_M2 gangliosides.