V sub(max.) activation of pp60 super(c-src) tyrosine kinase from neuroblastoma Neuro-2A

A kinetic analysis of the tyrosine-specific protein kinase of pp60 super(c-src) from the C1300 mouse neuroblastoma cell line Neuro-2A and pp60 super(c-src) expressed in fibroblasts was carried out to determine the nature of the increased specific activity of the neuroblastoma enzyme. In immune-complex kinase assays with ATP-Mn super(2+) and the tyrosine-containing peptide angiotensin I as phosphoacceptor substrate, pp60 super(c-src) from the neuroblastoma cell line was characterized by a maximum velocity (V sub(max.)) that was 7-15-fold greater than the V sub(max.) of pp60 super(c-src) from fibroblasts. The results indicate that the pp60 super(c-src) kinase from neuroblastoma cells has a higher turnover number than pp60 super(c-src) kinase from fibroblasts, and that the neural form of the enzyme would be expected to exhibit increased catalytic activity at the saturating concentrations of ATP that are found intracellularly.