Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Myosin-I refers to a class of proteins with a molecular weight of approximately 110-kDa, which have characteristics of conventional myosin but are unable to form filaments. Previous studies have implicated myosin-I in motile cellular processes including cell migration and phagocytosis. Although the first example of myosin-I in higher eukaryotes was the intestinal 110K-calmodulin complex, which forms in microvilli the lateral links connecting the core bundle of actin filaments to the membrane, myosin-I has now been shown to be a component of rat kidney and to be present in bovine adrenal gland and brain. We have now purified and characterized two polypeptides from rat liver which have several characteristics of the intestinal 110K-calmodulin complex. Both liver polypeptides are solubilized with ATP and co-elute on gel filtration with calmodulin. The polypeptides, of 110-kDa and 130-kDa, bind calmodulin in 1 mM EGTA. Both polypeptides bind to F-actin in an ATP reversible fashion, and crosslink actin filaments. The purified polypeptides possess an actin-activated Mg(2+)-ATPase activity typical of brush border myosin-I. A polyclonal antiserum directed against the chicken intestinal 110-kDa polypeptide recognizes both rat liver polypeptides, whereas another serum recognizes the 130-kDa but not the 110-kDa rat liver polypeptide. Controlled proteolysis of the purified polypeptides with alpha-chymotrypsin indicates that the two polypeptides are distinct but related. Immunofluorescence microscopy on isolated hepatocytes shows distribution of myosin-I to be vesicular, distributed throughout the cytoplasm, but more concentrated near the nucleus. These data contribute new evidence by several functional criteria that multiple myosin-I molecules are present in higher organisms and may coexist in a single cell type.
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PMID:Myosin-I in mammalian liver. 846 25

It is well established that the bioavailability of non-haem iron from foods is enhanced by the presence of meat. However, the nature of the promoter in meat has not yet been characterised. The present study was designed to compare the effects of the myofibrillar protein fractions on the bioavailability of non-haem iron in an attempt to identify the 'meat factor'. Rabbit skeletal muscle was fractionated and whole muscle, myofibrillar protein, myosin and actin were isolated. Myosin was subjected to selective proteolysis with chymotrypsin and the heavy meromyosin, light meromyosin, rod region and head region were prepared. Protein fractions (1 g) were incorporated into 100 g semi-synthetic liquid meal and the in vitro dialysability of iron was determined. Egg albumin was used as a reference protein. When compared with egg albumin, all protein fractions significantly enhanced iron dialysability, except for light meromyosin which was inhibitory. Myosin had a greater enhancing effect than actin and, within myosin, the enhancing effect was greatest for the heavy meromyosin fraction. The enhancement appeared to coincide with the known distribution of cysteine residues in the myofibrillar proteins. The presence of the sulphydryl blocking agent, N-ethylmaleimide (NEM), in meals containing myosin reduced iron dialysability in a dose-related manner, but NEM had only a small effect in meals containing actin. Meanwhile, incorporation of cysteine into meals containing actin increased iron dialysability. The present results suggest that the enhancement of non-haem iron dialysability by meat is associated with myosin, in particular, with the heavy meromyosin region. Peptide fractions rich in cysteine residues, probably constitutes the 'meat factor'.
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PMID:Effect of myofibrillar muscle proteins on the in vitro bioavailability of non-haem iron. 1061 59

Physicochemical changes and in vitro digestibility of chicken breast myosin oxidized with a nonenzymic free-radical-generating system (FeCl(3)/H(2)O(2)/ascorbate) were studied by SDS-PAGE, differential scanning calorimetry, and o-phthaldialdehyde assay. Oxidation caused fragmentation and polymerization of myosin. Myosin polymers were cross-linked mainly through disulfide bonds. Hydroxyl radicals destabilized myosin, lowering its denaturation temperature by up to 4 degrees C. Oxidized myosin also produced a new thermal transition in the 60-80 degrees C temperature range, which could be attributed to the formation of disulfide-stabilized polymers. The proteolytic susceptibility of myosin to pepsin, trypsin, and chymotrypsin was increased by oxidation. Under nonreducing conditions, however, oxidized myosin showed decreased digestibility. The results may help explain variations in the functionality and nutritional quality of muscle foods in meat processing in which oxidation is involved.
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PMID:Electrophoretic pattern, thermal denaturation, and in vitro digestibility of oxidized myosin. 1072 25


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