Troponin is unlikely to occur in bovine and chick forebrain

A search for the presence of troponin in brain reveals that troponin is below 0.00037% of total bovine brain soluble protein. Troponin levels were examined using G-actin-linked Sepharose affinity chromatography and 45Ca binding. The chromatographic and 45Ca binding experiments revealed the presence of several actin and calcium-binding proteins, none of which corresponded to any troponin subunit. In addition, troponin was not found in any chick brain subfraction analyzed, and the level of troponin in chick nerve ending cytoplasm enriched for troponin was less than 0.023%. Considering that substantial amounts of myosin and actin occur in brain, these findings indicate that troponin is not likely to be a regulator of putative brain actomyosin interactions. The significance of these results and their relation to proposed models for neurotransmitter release is discussed.