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The polymerization reaction of rabbit muscle actin was completely inhibited by reaction of one amino acid side chain per protein monomer with 5‐diazonium‐(1 H)[14C]tetrazole. A tryptic peptide fingerprint showed a single peptide labeled by the reagent. The peptide was isolated and the labeled amino acid identified by amino acid analysis as Tyr‐53. This side chain is not accessible to the reagent in F‐actin. The modification is compared to similar inhibitions by other reagents.

In a prospective clinical trial involving six patients suffering from essential thrombocythemia (ET), recombinant human interferon alpha 2b significantly and consistently lowered highly elevated peripheral platelet numbers over long time periods. One patient has now been on continuous treatment for 4 years. During the treatment phase none of the patients suffered from bleeding episodes, thrombosis or disturbances of the microcirculation. The interferon maintenance dose varies considerably from patient to patient, but it is usually much lower than the induction dose. One of the patients had to be withdrawn from the study due to interferon-specific chronic toxicity concomitant with the development of non-neutralizing interferon antibodies. With the exception of one patient, stopping interferon treatment led to an increase in peripheral platelet numbers of up to one million cells per microliter of blood within 4 to 12 weeks. We conclude that interferon alpha can correct peripheral thrombocytosis in selected patients with essential thrombocythemia over a period of years and prevent morbidity attributable to this disease.

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