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Titolo:
DIRECT DETERMINATION OF THE SUBSTRATE-SPECIFICITY OF THE ALPHA-ACTIVESITE IN HETERODIMERIC BETA-HEXOSAMINIDASE-A
Autore:
HOU YM; TSE R; MAHURAN DJ;
Indirizzi:
HOSP SICK CHILDREN,RES INST,555 UNIV AVE TORONTO ON M5G 1X8 CANADA HOSP SICK CHILDREN,RES INST TORONTO ON M5G 1X8 CANADA UNIV TORONTO,DEPT CLIN BIOCHEM TORONTO ON M5G 2C4 CANADA
Titolo Testata:
Biochemistry
fascicolo: 13, volume: 35, anno: 1996,
pagine: 3963 - 3969
SICI:
0006-2960(1996)35:13<3963:DDOTSO>2.0.ZU;2-1
Fonte:
ISI
Lingua:
ENG
Soggetto:
TAY-SACHS-DISEASE; HUMAN PLACENTAL HEXOSAMINIDASE; GM2 GANGLIOSIDOSIS; GM2-GANGLIOSIDOSIS-B1 VARIANT; N-ACETYLHEXOSAMINIDASE; PARAMETER-ESTIMATION; EXTENSIVE HOMOLOGY; ESCHERICHIA-COLI; SANDHOFF DISEASE; ADULT FORM;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
42
Recensione:
Indirizzi per estratti:
Citazione:
Y.M. Hou et al., "DIRECT DETERMINATION OF THE SUBSTRATE-SPECIFICITY OF THE ALPHA-ACTIVESITE IN HETERODIMERIC BETA-HEXOSAMINIDASE-A", Biochemistry, 35(13), 1996, pp. 3963-3969

Abstract

The beta-hexosaminidase isozymes are produced through the combinationof alpha and beta subunits to form any one of three active dimers (monomeric subunits are not functional). Heterodimeric hexosaminidase A (alpha beta) is the only isozyme that can hydrolyze G(M2) ganglioside in vivo, requiring the presence of the G(M2) activator protein. Hexosaminidase S (alpha alpha) exists but is not considered a physiological isozyme. Although hexosaminidase B (beta beta) is present in normal human tissues, it has no known unique function in vivo. However, a uniquefunction for the beta-active site present in both hexosaminidase A and B has been indicated in a previous study of the various substrate specificities of the homodimeric forms of hexosaminidase (S and B). It was concluded that the alpha-active site is only able to efficiently hydrolyze negatively charged substrates, and the beta-active site is only able to hydrolyze neutral substrates. When this model of nonoverlapping alpha- and beta-substrates is extrapolated to heterodimeric hexosaminidase A, it has a major effect on the interpretation of recent results relating to the mode of action of the G(M2) activator protein. In this report, we directly examine these substrate specificities using anovel form of hexosaminidase A containing an inactive beta subunit, produced in permanently transfected CHO cells. We demonstrate that, whereas the beta-active site has the same substrate specificities in either its A-heterodimeric or B-homodimeric forms, the alpha-active site in the A-heterodimer has different kinetic parameters than the alpha-active site in the S-homodimer. We conclude that the alpha and beta subunits in hexosaminidase A participate equally in the hydrolysis of neutral substrates.

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Documento generato il 01/12/20 alle ore 18:33:15