Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.26.9 (ribonuclease)
 6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have attempted to detect binding of N-acetylglucosamine (NAG) to alpha-lactalbumin, the B protein of lactose synthetase, under conditions in which binding of NAG to lysozyme, a protein to which alpha-lactalbumin has a significant sequence homology, is observed. Using 1H nuclear magnetic resonance spectroscopy, uv difference spectroscopy, competition of NAG with N-methylnicotinamide chloride, and fluorescence spectroscopy, no binding was detected. The synthesis of a NAG analogue, N-diazoacetyl-glucosamine (diazoNAG), was carried out, and the molecule was demonstrated to be an active galactose acceptor in the lactose synthetase reaction. Use of this molecule in photochemical labeling experiments resulted in a large amount of nonspecific labeling of alpha-lactalbumin, lactose synthetase A protein, ribonuclease, and lysozyme, but competition experiments in the presence of an excess of NAG revealed some specific labeling in the case of A protein and lysozyme, but not with alpha-lactalbumin or a ribonuclease control. Thus, it is highly questionable that a NAG binding site is retained in alpha-lactalbumin; furthermore, it appears that the galacyosyl acceptor makes significant contacts with the A protein rather than alpha-lactalbumin in the lactose synthetase complex.
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PMID:The interaction of N-acetylglucosamine and an affinity-label analogue with alpha-lactalbumin and lactose synthetase. 81 Dec 54

Galactosyltransferase (EC 2.4.1.22) requires bivalent metal ions for its activity. However, preparations of this enzyme solubilized from Golgi membranes of lactating rat mammary gland were shown to be activated not only by Mn2+, Ca2+ and Mg2+, but also by spermine, spermidine, lysyl-lysine, ethylenediamine and other diaminoalkanes, and by a range of basic proteins and peptides, including clupeine, histone, polylysine, ribonuclease, pancreatic trypsin inhibitor, cytochrome c, melittin, avidin and myelin basic protein. Both N-acetyl-lactosamine synthetase and lactose synthetase activities were enhanced. A basic protein fraction was isolated from bovine milk and shown to activate galactosyltransferase at low concentrations. The polyanions ATP, casein, chondroitin sulphate and heparin reversed the activation of galactosyltransferase by several of the above substances. Galactosyltransferase, assayed as a lactose synthetase, showed a 10-fold greater affinity for glucose when Mn2+ ions were replaced by clupeine or by ribonuclease as cationic activator. Evidence was obtained for the presence of an endogenous cationic activator in solubilized Golgi membrane preparations which evoked a similar low apparent Km,glucose. The findings are discussed in the light of cationic activations of glycosyltransferases generally, of the porous nature of the Golgi membrane, and of the unlikelihood of bivalent metal ions being the physiological activators of galactosyltransferase. It is suggested that the natural cationic activator of lactose synthetase may be a secretory protein acting in a manner analogous to the enzyme's activation by alpha-lactalbumin. A scheme is proposed for the two-stage synthesis of lactose and phosphorylation of casein within the cell, to accommodate the apparent incompatibility of these two processes.
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PMID:Cationic activation of galactosyltransferase from rat mammary Golgi membranes by polyamines and by basic peptides and proteins. 310 66