Synthetases lactose synthetase

Brodbeck and Ebner found that the soluble lactose synthetase from milk can be separated into two protein components, A and B, which individually do not exhibit any catalytic activity however, their recombination restores full lactose synthetase activity. The B fraction has been crystallized from bovine skim milk and bovine mammary tissue, and was identified as a-lactalbumin. It was thus found that a-lactalbumin can be substituted for the B protein of lactose synthetase. Lactose synthetases from the milk of sheep, goats, pigs, and humans were also resolved into A and B proteins, and the fractions from these species were shown to be qualitatively interchangeable in the rate assay of lactose synthesis. Determination of the amino acid sequence of a-lactalbumin (B fraction) has shown a distinct homology in the sequence of amino acids of a-lactalbumin and hen s egg-white lysozyme, suggesting that lysozyme and a-lactalbumin have evolved from a common ancestral gene. 

Brew, K., Shaper, J.H., Olsen, K.W., Trayer, I.P., and Hill, R.L. (1975) Cross-linking of the components of lactose synthetase with dimethylpimelimidate. J. Biol. Chem. 250, 1434-1444. 

Andrews, R, Kitchen, B.J., and Winzor, D., Use of affinity chromatography for the quantitative study of acceptor-ligand interactions The lactose synthetase system, Biochem. J., 135, 897-900, 1973. 

Figure 2.19 Sialylation ofN-acetyl lactose by cytidyl monophosphate-N-acetylneuraminic acid using Of 2,3-neuraminic acid transferase as catalyst (upper box). Regeneration of the sugar nucleotide is shown in the lower box. CMP is converted into CTP in two steps using two different kinases. In the final step CMP-A -acetylneuraminic acid is synthesised from CTP and A -acetylneuraminic acid (sialic acid) using the appropriate synthetase. The formed pyrophosphate is converted into inorganic phosphate. Altogether five different enzymes are involved in the process.

Bovine a-lactalbumin is one of the two enzymes in lactose synthetase, and its amino acid sequence shows striking similarities to that of lysozyme.118 A model based on the lysozyme model has been built, and the side-chain interactions found are convincing, showing that the model is essentially correct. The active cleft in the crystal is, however, shorter than that in the model, and is consistent with a mono- or di-saccharide as the substrate. Thus, the lysozyme structure may serve as a model for some enzymes that synthesize and hydrolyze carbohydrates. 

EC 2.4.1.22 Lactose synthetase UDP-galactose + D-glucose UDP + lactose Golgi apparatus SM... 

Denton, W. L. nd Ebner, K. E. 1971. Effect of tyrosyl modification on the activity of a-lactalbumin in the lactose synthetase reaction. J. Biol. Chem. 246, 4053-4059. 

Brew, K. 1969. Secretions of a-lactalbumin into milk and its relevance to the organization and control of lactose synthetase. Nature iLondon) 222, 671-672. 

Challand, G. S. and Rosemeyer, M. A. 1974. The correlation between the apparent molecular weight and the enzymic activity of lactose synthetase. Febs Letters 47, 94-97. 

In protein cross-linking studies, DMP has been used to examine the subunit structure of muscle pyruvate kinase (Davies and Kaplan, 1972), for the cross-linking of lactose synthetase (Brew et al., 1975), and to conjugate a fluorescent derivative of a-lactalbumin to glactosyltransferase (O Keefe et al., 1980). The reagent also has... 

In oligomeric proteins composed of nonidentical subunits, it is possible to determine the functional role of each subunit, if dissociation and isolation of subunits are attained in their native states. Examples are tryptophan synthase, lactose synthetase, and aspartate transcarbamoylase.25 ... 

In addition to its effects on synthesis of milk proteins themselves, prolactin also induces the production in the mammary gland of other proteins/enzymes involved in production of milk components. Lactose synthetase and enzymes of lipid metabolism, including acetyl-CoA carboxylase and lipoprotein lipase, are among these inducible enzymes [75]. 

Q -Lactalbumin (a-LA) is a component of mammalian milk. It complexes with jS-galactosyl transferase to form lactose synthetase that catalyzes the synthesis of lactose. Unlike most of the other known calcium-binding proteins that have clusters of calcium ions or cooperative calcium binding, only one calcium-binding site with very high calcium-binding... 

In the early 1960s Hassid and collaborators demonstrated that the enzyme lactose synthetase (now synthase) exists as a microsomal enzyme in the mammary glands of lactating cows and guinea pigs (Watkins and Hassid, 1962) and in a soluble form in cow milk (Babad and Hassid, 1964, 1966). They confirmed an earlier suggesdon by Wood and co-... 

Figure 2 One-pot three-enzyme chemoenzymatic synthesis of sialosides containing sialic acid modifications. In this strategy, mannose or ManNAc derivatives are chemically or enzymatically synthesized. These compounds are then used by a recombinant coli K-12 sialic acid aldolase to obtain sialic acids and their derivatives followed by an N. meningitidis CMP-sialic acid synthetase for the formation of CMP-sialic acids. From which, sialic acids can be transferred to lactose, LacNAc, galactose, GalNAc, or their derivatives by a multifunctional P. muitocida sialyltransferase (PmSTl) or a P, damseia a2,6-sialyltransferase (Pd2,6ST) to form a2,3- or a2,6-linked sialosides in one pot without the isolation of intermediates.

As another example, the s subunit of bacterial RNA polymerase provides specificity for particular substrate (DNA) sequences. Also, lactose synthetase in the mammary gland has its reaction altered by binding of a protein subunit. 

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