Evidence for Calcium‐sensitive Component in Brain Actomyosin‐like Protein (Neurostenin)

The isolation of brain actomyosin‐like protein (neurostenin) with a Ca2+ ‐sensitive component is described. The addition of 1 mm EGTA results in approximately 50 per cent reduction in MgATPase activity. The inhibition can be released by a free Ca2+ concentration of 10−6m. Dialysis of the protein complex against low ionic strength medium followed by centrifugation results in a loss of Ca2+ sensitivity in the pelleted protein. Ca2+ sensitivity can be restored by reprecipitating this desensitized complex in the presence of the 70.000 g supernatant. The protection of sulphhydryl groups during desensitization and reconstitution procedures is essential. This Ca2+ regulatory property is similar, in these respects, to other actomyosin‐like proteins.