Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Titin and nebulin are two major protein components of a cytoskeletal matrix that coexists with thick and thin filaments within the sarcomere of a wide range of striated muscles. Purified titin and nebulin from mouse diaphragm muscle are similar in size, in relative abundance, and in amino acid composition to analogous proteins from other mammals or avians. Phosphate analysis of these nucleic-acid-free proteins indicated that both proteins contain substantial amounts of protein-bound phosphate: about 12 mol of phosphate per mole of titin subunit and 11 mol of phosphate per mole of nebulin subunit. Incubation of intact, excised mouse diaphragm with radioactive inorganic phosphate resulted in significant incorporation of radiophosphate into titin and nebulin. The identification of titin and nebulin phosphorylation was facilitated by a simple salt fractionation and nuclease digestion procedure that effectively separated titin and nebulin from radiolabeled nucleic acids. Such in vivo phosphorylation studies indicated that approximately 2 mol of phosphate per titin subunit and 5 to 7 mol of phosphate per nebulin subunit were incorporated within 5 h of incubation. The incorporation nearly doubled when the beta-adrenergic agonist, isoproterenol, or a phosphodiesterase inhibitor, theophylline, was present in the medium. For both proteins, phosphorylation occurred mainly on serine residues. Nebulin also appears to possess a smaller number of threonine sites. Taken together, our data indicate that a small proportion (20 to 40%) of the steady-state titin phosphates are rapidly turning over. In contrast, most of the nebulin phosphates (50 to 100%) are readily exchanged. The modulation of turnover by external stimuli that increase cytosolic cAMP raises the possibility that at least a portion of the multiple phosphorylation sites of titin and nebulin may be involved in the functional regulation of the sarcomere matrix.
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PMID:Sarcomere matrix of striated muscle: in vivo phosphorylation of titin and nebulin in mouse diaphragm muscle. 335 62

Titin and nebulin are two major protein components of the sarcomere matrix in striated muscles. Purified titin and nebulin from frog (Xenopus laevis) skeletal muscle are similar in size and in amino acid composition to their mammalian or avian counterparts. Both proteins contain substantial amounts of protein-bound phosphate: about 5 to 6 per titin subunit and 8 to 9 per nebulin subunit. Injection of radioactive inorganic phosphate into the dorsal lymph sacs of Xenopus laevis resulted in the significant incorporation of radioactivity into titin and nebulin within three days of incubation. Purified titin from in vivo labeled frog gastrocnemius muscle contains one mole of radioactive phosphoserine per mole of titin subunit. These data indicate that phosphorylation of frog titin and nebulin occurs in vivo.
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PMID:In vivo phosphorylation of titin and nebulin in frog skeletal muscle. 366 25