Fig. 5. (A) Identification of troponin T (TnT) S1 and S2 isoforms in brook trout based on hydroxy-apatite chromatography and a silver-stained PAGE gel. Lane 1 is a ladder of protein standards (BioRad), and lane 2 is the 75 mmol l^–1 phosphate hydroxy-apatite column fraction that contains two isoforms of purified rainbow trout red muscle TnT, identified as TnT S1 and S2. (B) Myofibrillar proteins in a representative brook trout. Partially purified myofibrillar proteins ranging in size from myosin heavy chain at the top of the gel (largest protein visible) to putative parvalbumin at the bottom of the gel (smallest protein visible). Lanes 1–3 contain purified myofibrils from 35, 55 and 75% of total length from the snout. Lane 4 contains a ladder of protein standards. There is some indication of longitudinal variation in a protein at 33–34 kDa (tropomyosin?, see diamond-head arrow). At the anterior position (35% TL) there is a doublet, but the middle and posterior positions show only a single band. No other obvious longitudinal variations are observed here or in other gels except for variations in TnT. (C) TnT expression in a representative brook trout. Magnification of the bands from B. Red muscle TnT isoforms were identified based on size using a Sypro Ruby-stained PAGE gel. The two visible bands are the brook trout red muscle TnT isoforms. In this individual, relative expression levels (as indicated by staining intensity) for the lower band (TnT 2S) increase from anterior to posterior of the fish.