Superfast-contracting muscle fibres (II M) were identified by ATPase staining and after incubation with an antiserum raised against myosin type II M and with an antibody raised against the Galα1–3Galβ1–4GlcNAc structure. II M fibres were present in masseter muscles from cat, dog andMacaca fascicularisbut not in limb muscles from the same animals and not in masseter muscles from rat, pig, cow or man. Electrophoresis and staining of blots from myosin preparations showed that the anticarbohydrate antibody detected myosin heavy chains from cat masseter but not myosin heavy chains from cat biceps. The α-galactose specific lectinGriffonia simplicifoliaisolectin B4 (GS I B4) did not stain muscle fibres or myosin heavy chains. Therefore, the epitope on myosin heavy chains defined by the anticarbohydrate antibody is presumably not Galα1–3Galβ1–4GlcNAc although the antibody staining was strongly inhibited after absorption by 10 mM of this trisaccharide. Antibody staining of the muscle fibres was totally inhibited by adding 10 mM p-nitrophenyl β-D-glucuronide to the incubation medium. The results thus imply that an anticarbohydrate antibody distinctively detects a carbohydrate epitope specific for myosin in superfast contracting muscle fibres from jaw-closing muscles and confirm that this epitope is not present in other muscle fibre types. This appears to be the first report on differentiated glycosylation amon
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