Characterization of activity of alkaline phosphatase (AAP) in capillary endothelium of normal and psoriatic skin.

The activity of alkaline phosphatase (AAP) in papillary capillaries of normal and psoriatic skin was characterized by enzyme inhibition studies. Quantitatively, there were pronounced differences between normal and psoriatic skin, i.e., increase of AAP, as determined by a grading system, and assimilation of the strength of AAP in venous and arterial side of the capillary loop in psoriasis. Qualitatively, the inhibition studies with different actin inhibitors revealed no difference between AAP in normal and psoriatic skin or between initial, fully developed and healed psoriatic lesions as well as noninvolved skin of psoriatics. Thus, the physiologic AAP seems to be stimulated in psoriasis. Generally, AAP of dermal capillaries is highly sensitive to cysteine inhibition.