Ultraviolet photoinactivation of galactosyltransferase. Protection by substrates

Galactosyltransferase was irreversibly inactivated upon exposure to ultraviolet light and the rate of inactivation followed apparent first-order kinetics. Significant protection against inactivation was observed in the presence of various combinations of substrates. UDPgalactose and Mn2+ together ga...

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Veröffentlicht in:Biochemistry (Easton) 1976-03, Vol.15 (5), p.1093-1097
Hauptverfasser: Clymer, David J, Geren, Collis R, Ebner, Kurt E
Format: Artikel
Sprache:eng
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Zusammenfassung:Galactosyltransferase was irreversibly inactivated upon exposure to ultraviolet light and the rate of inactivation followed apparent first-order kinetics. Significant protection against inactivation was observed in the presence of various combinations of substrates. UDPgalactose and Mn2+ together gave the most protection. Amino acid analyses revealed the loss of 1 mol of tryptophan per mol of galactosyltransferase upon ultraviolet photoinactivation. Further evidence for an essential trypotphan was provided by difference spectra and by inactivation with 2-hydroxy-5-nitrobenzyl bromide and protection against this reagent by Mn2+ and UDPgalactose. The protection by UDPgalactose and Mn2+ was greater than that provided by UDPgalactose alone. Since Mn2+ provided no protection by itself, this suggested that the formation of the galactosyltransferase-Mn2+-UDPgalactose complex caused a conformational change which was responsible for the observed protection of the essential tryptophanyl residue.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00650a022