High tyrosine protein kinase activities were detected in soluble and particulate forms from bone marrow cells using synthetic peptide (Glu-Asp-Ala-Glu-Tyr-Ala-Ala-Arg-Arg-Arg-Gly) as a substrate. Total activity of tyrosine protein kinase was 2.4 times higher in the soluble fraction but the specific activity was slightly higher in the particulate one. Mg2+ or Mn2+ requirements of these two enzymes for maximal activity were quite different from each other. Physiological significance of these two forms of enzymes is briefly discussed.
