An enzymatic assay for available zinc in plasma and serum

A convenient enzymatic assay for available zinc in plasma and serum was developed. The assay is based upon the reactivation of the zinc metalloenzyme alkaline phosphatase which had been previously inactivated by nitrilotriacetic acid. The enzymatic assay was applied to serum samples from human subjects in a study of zinc utilization in pregnancy and to plasma samples from rats in a zinc deficiency study. Most plasma samples with low zinc levels (less than 70 microgram/dl) reactivated the enzyme to less than 30% of control activity. Most samples with normal zinc levels (70-120 microgram/dl) reactivated the enzyme 30-65%. Samples with elevated zinc levels (greater than 120 microgram/dl) reactivated the enzyme over 70%. The assay is quick, convenient, and in principle measures functionally available zinc.