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.
No takes yet. Share an insight, caveat, or question.
Clymer et al. (1976) studied this question.
Synapse has enriched 4 closely related papers on similar clinical questions. Consider them for comparative context: