Characterization of human placental beta-hexosaminidase I2. Proteolytic processing intermediates of hexosaminidase A
The lysosomal hydrolase beta-hexosaminidase (beta-N-acetylhexosaminidase, EC 3.2.1.52) exists as two major isozymes in normal human tissue: an acidic A-form and a basic B-form. There are also minor forms of intermediate pI known as I-forms. Increases in one or more of these intermediates have been a...
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Veröffentlicht in: | The Journal of biological chemistry 1990-04, Vol.265 (12), p.6794-6799 |
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Sprache: | eng |
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Zusammenfassung: | The lysosomal hydrolase beta-hexosaminidase (beta-N-acetylhexosaminidase, EC 3.2.1.52) exists as two major isozymes in normal
human tissue: an acidic A-form and a basic B-form. There are also minor forms of intermediate pI known as I-forms. Increases
in one or more of these intermediates have been associated with various disease states. Although the two major isozymes have
been extensively studied, the structure and biosynthetic origins of the I-forms are unknown. Characterization of a placental
hexosaminidase I-form, presented in this report, demonstrates that it is composed of two forms of partially processed hexosaminidase
A. The major form contains an intact pro-alpha chain and a pro-beta chain lacking 2 residues from its amino terminus (Ala
and Arg). The minor form also contains an alpha and a beta subunit, but each has undergone further proteolytic processing.
The amino terminus of each of these partially processed polypeptide chains matches one of those previously found on stable
processing intermediates in a single normal human fibroblast cell line. These data confirm that similar processing intermediates
exist in human placenta, suggesting that this I-form lacks a unique enzymatic function in vivo. A sequence of normal proteolytic
processing events is postulated. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/S0021-9258(19)39219-1 |