A Sensitive Microassay for Prolyl Hydroxylase: Activity in Normal and Psoriatic Skin

A sensitive micromethod for the assay of prolyl hydroxylase (PH), an enzyme essential for the biosynthesis of collagen, has been developed and used to assess levels of the enzyme in small specimens of normal and pathologic skin. By employing a substrate highly labeled with 3, 4-3H proline and a reduced reaction volume, we have increased the sensitivity of the assay by approximately thirtyfold. The levels of PH in human skin vary by site. Activity in trunk skin, for example, is considerably higher than in forearm skin. Thus, site-matched controls are essential when assessing enzyme levels in disease states. Infiltration of the biopsy site with xylocaine reduces PH activity, indicating that results obtained from specimens containing a local anesthetic must be interpreted with caution. Prolyl hydroxylase levels in psoriatic lesions are approximately fourfold greater than those in normal control or uninvolved psoriatic skin. Since the collagen content of psoriatic skin in normal, increased turnover of collagen in psoriasis may be present.