The D. W. B. A. for Cr52 (d, p) Cr53 reactions with measured optical model parameters

Andrews, P T; Clifft, R. W.; Green, L.L.; Sharpey‐Schafer, J. F.

doi:10.1016/0031-9163(62)90021-5

Cited by 6 publications

(1 citation statement)

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“…Estimates of the association constants for the binary complexes were 2 . lo2 M-' and 0.6 M-' for the galactosyl transferase with N-acetylglucosamine and glucose respectively [28]. Therefore the role of a-lactalbumin is to enhance the association by approximately the same extent in both cases.…”

Section: Imp/ications Of Complex Formationmentioning

confidence: 90%

Lactose Synthetase

1976

European Journal of Biochemistry

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Galactosyl transferase and cc-lactalbuniin were concurrently isolated from bovine milk. The galactosyl transferase had an s20,w of 3.0 S and D20,w of 60 pm2/s. It exists as a monomer of 46 000 molecular weight, as determined by sedimentation equilibrium and dodecylsulphatepolyacrylamide electrophoresis. Aggregation of the enzyme was promoted by N-acetylglucosamine.Sedimentation velocity experiments show an association between galactosyl transferase and a-lactalbumin in the presence of N-acetylglucosaniine. In contrast, UDP-galactose, UDP or lactose do not promote protein-protein association.A complex between galactosyl transferase and x-lactalbumin was isolated by gel filtration in the presence of excess a-lactalbumin and either N-acetylglucosamine or glucose. The complex was stable over a range of concentrations of these components.The complex is a discrete homogeneous entity with a molecular weight of 60000, corresponding to one molecule of galactosyl transferase and one molecule of x-lactalbumin.The estimated association constants for the ternary complexes of the two proteins and either of the sugars, suggest that a-lactalbumin enhances equally the binding of N-acetylglucosamine or glucose to the galactosyl transferase. amine is low in the galactosyl transferase reaction, and the addition of a-lactalbumin promotes a substrate U DP-galactose UDPThe presence of protein B inhibits this second reaction [3]. Therefore the B protein, identified as cc-lactalbumin [4], which alone has no known catalytic activity, was proposed as a 'specific' or 'modifier' protein [3], which directs the galactosyl transferase to the sythesis of lactose rather than of N-acetyllactosamine. However, terms such as 'modifier' are not meaningful unless there is evidence for the mechanism whereby the protein produces its effect. Also, the switch from one reaction to the other is not absolute, but depends on the substrate conceninhibition [6] at the concentrations of sugar normally used in the assay. Both the enhancement of the reaction with glucose and the inhibition of the reaction with N-acetylglucosamine could arise from an increase in monosaccharide binding mediated by a-lactalbumin [61.A possible method for mediation by x-lactalbumin between the galactosyl transferase and the sugar substrates is by the formation of a protein-protein complex. Attempts to obtain such a complex have been unsuccessful [S, 91. Nevertheless an interaction between the two proteins is implicit in the method used to isolate the galactosyl transferase by affinity chromatography [I 01, since a-lactalbumin, covalently bound to a matrix, retains galactosyl transferase in filtration data [lo], and was also inferred from sedi-

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Section: Imp/ications Of Complex Formationmentioning

confidence: 90%