The chemotactic peptide fmet-leu-phe and the Ca2+-ionophore A23187, stimulate PMN tubulin tyrosinolation that is dependent on the presence of extracellular Ca2+ and the activation of NADPH-oxidase mediated oxidative burst. Isolated PMN cytoplasts (CP) and karyogranuloplasts (KGP) fail to respond to either stimuli, indicating the requirement of an intact functional PMN for the modulation of PMN tubulin tyrosinolation. Unlike the specific stimulation of tubulin tyrosinolation in fmet-leu-phe or A23187-stimulated PMN, an intriguing phenomenon of tyrosine incorporation into multiple proteins was observed in PMA-activated PMN, that is dependent on the pathway for NADPH-oxidase activation and independent of protein synthesis. The reaction is inhibited by a variety of reducing agents and intracellular scavengers of oxygen radicals. PMA-activated PMN from patients with chronic granulomatous disease failed to exhibit this phenomenon, but activated PMN from a myeloperoxidase deficient patients incorporated the tyrosine. PMA-activatiion of PMN causes a two-fold increase in the generation of protein carbonyl derivatives, which is potentiated in the presence of labeled tyrosine. Reverse phase HPLC analysis of radiolabeled samples indicate the presence of radioactivity in multiple peaks with distribution throughout the protein (peptide) fractionation range. SDS-urea gel patterns also reveal similar results. The PMA-induced incorporation of tyrosine is highly exaggerated in KGP and also appears to be quite specific for tyrosine as other amino acids like phenylalanine, leucine, histidine or methionine, fail to incorporate. The biochemical mechanism and the functional role of this intriguing reaction remains to be elucidated.
