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Lactose Synthesis: The Possibilities of Regulation

Department of Biochemistry, University of Birmingham, Birmingham B15 2TT, U.K.

ABSTRACT

Elucidation of the details of lactose synthesis, in particular its dependence upon -lactalbumin and its location within the lumen of the Golgi apparatus, now allows one to ask useful questions pertaining to its regulation. Attention is directed towards galactosyltransferase itself (EC 2.4.1.22), which appears to be rate-limiting in the uridine nucleotide cycle that supports lactose synthesis, and to those factors that may affect its activity. In laboratory animals -lactalbumin appears to be the major agent of regulation during lacto-genesis but is not necessarily limiting at other times, whereas the increase in amount of galactosyltransferase seems largely to account for the rising yield of lactose during lactation. Studies with pinched-off Golgi membrane vesicles, together with measurements of intracellular chemical concentrations, suggest that (ß-glucose and uridine diphosphate-galactose do not saturate lactose synthesis and are, therefore, potentially regulatory features of this process. Further aspects of lactose synthesis that may offer points of regulation include calcium ions, generation of protons within the Golgi lumen, and the generally rate-limiting nature of the Golgi membrane.

² The Radiochemical Centre, White Lion Road, Amersham, Little Chalfont, U.K.

² Department of Biochemistry, University of Notingham, Clifton Boulevard, Nottingham, U.K.

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