AVAILABILITY OF SPECIFIC SUGARS FOR GLYCOCONJUGATE BIOSYNTHESIS - A NEED FOR FURTHER INVESTIGATIONS IN MAN

We review the metabolism of specific sugars used for protein glycosyla tion, focusing on the fate of exogenously provided sugars. Theoretical ly, all glycoprotein sugars can derive from glucose, but previous stud ies show that other exogenous sugars can be incorporated into glycopro teins. From data obtained in congenital galactosemia, exogenous galact ose may be important for correct glycosylation. Contrary to galactose, the metabolism of other sugars seems to depend on insulin regulation: stimulation of their endogenous production in diabetic subjects might participate in some diabetic complications, precluding the need for a n exogenous supply. The metabolic fate of these sugars is different ac cording to the administration route and exogenous supply may be import ant either in enteral nutrition or in some clinical situations as has been suggested for sialic acid in the newborn. Data in man are too spa rse to reach firm conclusions, implying a need for further investigati ons. Our preliminary results in animals and man demonstrate that stabl e isotope methodology allows one to trace glycoprotein sugar metabolis m in nutritionally relevant conditions with accuracy and sensitivity, using doses of specific sugars well below toxic levels. ((C) Societe f rancaise de biochimie et biologie moleculaire/Elsevier, Paris).