Characterization of tyrosyl kinase activity in human serum

Abstract

Tyrosyl kinase activity was detected in 1.0 microliter or less of human serum with the substrates angiotensin II, polyamino acid polymer Glu-Tyr (4:1), anti-pp60src IgG, and endogenous serum proteins. Most (about 84%) of the tyrosyl kinase activity was in the 100,000 X g soluble fraction from serum and a similar level of activity was found in the soluble fraction from plasma. Expression of tyrosyl kinase activity in individual serum samples differed more than 15-fold. The different levels of tyrosyl kinase activity were not likely due to phosphatases, proteases, ATPases, or kinase inhibitors and activators in serum. The normal serum and plasma tyrosyl kinase activities were not stimulated by epidermal growth factor, platelet-derived growth factor, insulin, or growth factors from fetal calf serum. Investigations of samples from patients with malignant disorders indicated that those with malignant melanoma contained the highest levels of serum tyrosyl kinase activity.