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. 1974 Jul;141(1):173–178. doi: 10.1042/bj1410173

Studies on the thiol group of lactose synthetase A protein from human milk and on the binding of uridine diphosphate galactose to the enzyme

B J Kitchen 1, P Andrews 1
PMCID: PMC1168064  PMID: 4375968

Abstract

The lactose synthetase activity of A protein from human milk was much decreased but not abolished by reaction with thiol-group reagents. Protection experiments indicated that a free thiol group on the enzyme is situated near the UDP-galactose binding site and inactivation of the enzyme with p-hydroxymercuribenzoate was probably due to prevention of UDP-galactose binding. Affinity chromatography showed that the mercuribenzoate substituent also decreased the affinity of A protein for N-acetylglucosamine but complex-formation between A protein–N-acetylglucosamine and α-lactalbumin was relatively unaffected. UDP-galactose appears to be bound to the enzyme mainly through its pyrophosphate group with Mn2+ ion and through the cis hydroxyls of ribose, whereas its hexose moiety has little if any affinity for the enzyme. Lactose synthetase activity remaining after the reaction with thiol-group reagents indicates that a free thiol group is not an essential part of the A protein active site.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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