Incorporation of D-(3H)glucosamine into normal and psoriatic epidermal glycoconjugates

Samples of normal, uninvolved and involved psoriatic skin were maintained for 18 h in organ culture in the presence of D-(6-3H) glucosamine which is a precursor of cell-surface associated carbohydrates in the epidermis. The total incorporation into involved psoriatic epidermis (solubilized with 8 mol/l urea, 5% sodium dodecyl sulphate, 10 mmol 2-mercaptoethanol) was less than into normal or uninvolved epidermis. This decrease was found whether specific radioactivities were expressed in terms or area, wet weight or protein content of the epidermis. Electrophoresis revealed that the major labelled component in normal and uninvolved epidermis had a high molecular weight. The labelling of this material was significantly reduced in involved psoriatic epidermis. Using pig epidermis we have shown previously that this material represents mainly extracellular glycosaminoglycans and proteoglycans. The decrease labelling (and presumable synthesis) of these extracellular carbohydrates may be related to the failure of mechanisms controlling cell proliferation and to the altered cell interactions which are found in psoriatic epidermis. Electrophoresis also showed that a non-glycosylated protein, molecular weight approximately 50,000, which was present as a singly band in both normal and uninvolved epidermis was always present as a doublet band in the involved psoriatic epidermis.