Tropomyosin isoform expression and phosphorylation in the human heart in health and disease

We determined the isoforms of tropomyosin expressed and the level of tropomyosin phosphorylation in donor, end-stage failing and hypertrophic obstructive cardiomyopathy samples of human heart muscle. Western blots and isoform-specific antibodies showed that α-tropomyosin was the only significant isoform expressed and that tropomyosin was 25-30% phosphorylated at serine 283. Mass spectrometry confirmed directly that α-tropomyosin made up over 95% of tropomyosin but also indicated the presence of up to 4% κ-tropomyosin and much smaller amounts of β-, γ- and smooth β-tropomyosin and about 26% phosphorylation. Neither the isoform distribution nor the level of phosphorylation changed significantly in the pathological heart muscle samples.