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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Degradation rates of muscle proteins were determined in young rats allowed access to standard rat chow 12 h/day. degradation was assessed by determination of 3-methylhistidine (3MH) excretion rates. 3MH is a nonreutilized amino acid produced almost exclusively within the actin and myosin of skeletal and cardiac muscle. Because plasma levels of 3MH are low and renal clearance is high, excretion reflects myofibrillar degradative rates. Excretion of 3MH was determined for 4-h periods beginning 12 and 20 h after initiation of feeding and after 24-and 48-h fasts. Excretion of 3MH per 4-h period increased with time after the last feeding. Because creatinine excretion is a function of muscle mass dividing 3MH excretion by creatinine excretion represents myofibrillar degradation per unit muscle mass, the fractional degradative rate. Degradation rates rose from 4.6 to 14.5%/day between 12 and 16 and 60 and 64 h after the beginning of the last meal. These results support the presence of a diurnal pattern of protein degradation as well as increased muscle degradation during starvation.
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PMID:Protein degradation in muscle: response to feeding and fasting in growing rats. 88 48

The content of myosin in plasmodia of the myxomycete Physarum polycephalum was measured by an immunological technique, quantitative microcomplement (C') fixation. Migrating plasmodia (starved after growth on rolled oats) contained 0.60 +/- 0.08 (SD) mg myosin per g fresh plasmodia. Myosin comprised 0.77% +/- 0.05 (SD) of the total plasmodial protein. When total plasmodial proteins were separated by electrophoresis on SDS-polyacrylamide gels, a large amount of protein appeared in a band comigrating with muscle actin. Densitometry performed after Coomassie blue staining indicated that as much as 15-25% of the total protein in the plasmodium could be actin. This gives an actin/myosin ratio by weight in the myxomycete plasmodium as high as 19-33, a very "actin-rich" actomyosin compared with rabbit skeletal muscle actomyosin with an actin/myosin ratio of 0.6. Starvation stimulates rapid migration and is correlated with a higher percent of both myosin and actin in the total protein of the plasmodium compared with normally growing cultures. Immunological cross-reaction of myosins from a variety of species was measured by C' fixation using an antiserum produced against purified native myosin from P. polycephalum. Although myxomycete and vertebrate striated muscle myosins have very similar morphological and biochemical properties, and apparently possess similar binding properties to F-actin, only myosins from myxomycetes in the order Physarales, rather closely related to P. polycephalum, gave detectable cross-reactions. This finding suggests that many amino acid sequences in myosin have been variable during evolution.
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PMID:Actomyosin content of Physarum plasmodia and detection of immunological cross-reactions with myosins from related species. 94 88

We have cloned and completely sequenced a gene encoding the heavy chain of Dictyostelium myosin I. Like the myosin I molecules from Acanthamoeba, the Dictyostelium myosin I heavy chain is composed of a globular head domain fused to a 45-kDa glycine-, proline-, and alanine-rich carboxyl-terminal domain, rather than the coiled-coil rod domain of conventional myosins. Comparisons of the Dictyostelium myosin I heavy-chain amino acid sequence with those of the Acanthamoeba myosins I reveal that they are highly similar throughout, including the unconventional carboxyl-terminal domains. The Dictyostelium myosin I gene is expressed in growing cells as a 3600-nucleotide mRNA. Measurements of the steady-state level of this mRNA at different times during starvation-induced aggregation and development are consistent with a role for myosin I in chemotaxis and aggregation. Generation of Dictyostelium cells lacking myosin I by gene disruption and/or antisense RNA production should provide a way to test directly the role of this nonfilamentous myosin in cell motility. These experiments will be simplified by the fact that Southern blot analyses of Dictyostelium genomic DNA are consistent with there being a single myosin I heavy-chain gene.
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PMID:Dictyostelium discoideum contains a gene encoding a myosin I heavy chain. 276 20

Saithe (Pollachius virens L.) were starved for 66 days at 10 degrees C and activities of aryl sulfatase, acid proteinase, beta-glucuronidase, RNAase and acid phosphatase measured in homogenates prepared from fast and slow myotomal muscles. In fed fish, hydrolase activities were generally higher in slow than fast muscles. With the exception of acid proteinase activity in slow muscle, the activities of all the lysosomal enzymes increased by 70 to 100% during starvation. In general, there was a proportionally larger increase in the hydrolase activities in fast than in slow muscle. In a second experiment, fish were starved for 74 days, and refed for up to 52 days. The increases in aryl sulfatase and acid proteinase activity produced in fast muscle with starvation were found to be rapidly reversed by refeeding. Lysosomal enzyme activities in fish sampled after 10 days refeeding were not significantly different from fed controls. Membrane fractions enriched in aryl sulfatase activity were prepared from the fast muscle of 66-day starved fish. These were capable of degrading both myosin heavy chains and actin to lower molecular weight peptides at acid (pH 5.0), but not at neutral pH. The results suggest a role for lysosomal enzymes in the breakdown of myofibrillar proteins during starvation.
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PMID:Lysosomal enzyme activities in muscle following starvation and refeeding in the saithe Pollachius virens L. 391 Apr 36

The actomyosin protein complex of Physarum polycephalum was prepared from vegetative and starved plasmodia. The yield of actomyosin per unit wet wt. was the same from both types of plasmodia. Myosin was resolved from the complex by gel filtration and purified by ion-exchange chromatography. The Ca(2+)-stimulated adenosine triphosphatase activities of myosin preparations from vegetative and starved plasmodia were not appreciably different. Synthesis of myosin de novo was shown to occur during the starvation phase of the life-cycle by the isolation of labelled myosin preparations from plasmodia starved in the presence of [2-(14)C]glycine. Fractionation of polyacrylamide gels after gel filtration of labelled myosin confirmed the presence of label in the adenosine triphosphatase-active myosin band. It is concluded that during starvation myosin synthesis continues although there is a net loss of approx. 50% of the total protein. Sodium dodecyl sulphate-polyacrylamide-gel electrophoresis of Physarum myosin showed the presence of low-molecular-weight components of the molecule, similar to those of muscle myosins. The content and composition of the free amino acid pool of Physarum was measured at various time-intervals during the vegetative and starvation phases of the life-cycle.
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PMID:The biosynthesis of plasmodial myosin during starvation of Physarum polycephalum. 427 85

The turnover of 3-methylhistidine (N tau-methylhistidine) and in some cases actin, myosin heavy chain and aldolase in skeletal muscle was measured in a number of experiments in growing and adult rats in the fed and overnight-starved states. In growing fed rats in three separate experiments, measurements of the methylation rate of protein-bound 3-methylhistidine by either [14C]- or [3H]-methyl-labelled S-adenosylmethionine show that 3-methylhistidine synthesis is slower than the overall rate of protein synthesis indicated by [14C]tyrosine incorporation. Values ranged from 36 to 51%. However, in one experiment with rapidly growing young fed rats, acute measurements over 1 h showed that 3-methylhistidine synthesis could be increased to the same rate as the overall rate. After overnight starvation in these rats, the steady-state synthesis rate of 3-methylhistidine was 38.8% of the overall rate. This was a similar value to that in adult non-growing rats, in which measurements of the relative labelling of 3-methylhistidine and histidine after a single injection of [14C]histidine indicated that 3-methylhistidine synthesis was 37% of the overall rate in the fed or overnight-starved state. According to measurements of actin, myosin heavy-chain and aldolase synthesis in the over-night-starved state with young rats, with a variety of precursors, slow turnover of 3-methylhistidine results from the specific slow turnover of actin, since turnover rates of myosin heavy chain, mixed protein and aldolase were 2.5, 3 and 3.4 times faster respectively. However, in the fed state synthesis rates of actin were increased disproportionately to give similar rates for all proteins. These results show that (a) 3-methylhistidine turnover in muscle is less than half the overall rate in both young and adult rats, (b) slow 3-methylhistidine turnover reflects the specifically slow turnover of actin compared with myosin heavy chain and other muscle proteins, and (c) during growth the synthesis rate of actin is particularly sensitive to the nutritional state and can be increased to a similar rate to that of other proteins.
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PMID:Myofibrillar protein turnover. Synthesis of protein-bound 3-methylhistidine, actin, myosin heavy chain and aldolase in rat skeletal muscle in the fed and starved states. 661 82

Urinary excretion of the post-translationally modified amino-acid 3-methylhistidine, derived from the contractile proteins actin and myosin, was measured in patients with conditions associated with nitrogen loss. The ratio of 3-methylhistidine:creatinine excretion, a measure of the fractional catabolic rate of myofibrillar protein was increased in severe injury, thyrotoxicosis, neoplastic disease, prednisolone administration, and sometimes Duchenne muscular dystrophy. In myxoedema, osteomalacia, and hypothermia the ratio was decreased; and starvation, elective operations, and rheumatoid arthritis had little effect. Provided that the diet is meat free, measurement of urinary 3-methylhistidine may provide useful information on the cause of protein loss.
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PMID:Clinical usefulness of urinary 3-methylhistidine excretion in indicating muscle protein breakdown. 678 20

Dictyostelium amoebae that lack myosin II (mhcA-) are unable to undergo morphogenesis. The cells aggregate slowly to form hemispherical mounds, but the mounds never extend a tip upward. Expression of developmentally regulated genes appears normal in the absence of morphogenesis. When mixed with an excess of wild-type cells, some mutant cells form differentiated spores; however, rescue is extremely inefficient (Knecht and Loomis, 1988). In order to assess how morphogenesis is normally accomplished and why mutants lacking myosin II cannot develop, a new method has been developed that allows individual amoebae to be localized and tracked at high resolution within the multicellular organism during development. Amoebae are labeled with a fluorescent dye at the beginning of starvation, mixed with an excess of unlabeled cells, and allowed to develop. The three-dimensional position of labeled cells in the multicellular organism is then determined using a laser scanning confocal microscope. Using this methodology, we have shown that labeled wild-type cells are randomly distributed throughout the organism and complete development normally. When labeled mhcA- mutant cells are mixed with a 20-fold excess of wild-type cells, they are non-randomly localized even at the earliest stages of development. Mutant cells in aggregation streams are found primarily at the edges of the streams and many cells never become part of the streams or are left behind as the wild-type cells complete aggregation. Those that are incorporated into the aggregate are found at the edge and base, the backs of slugs and the base of the fruiting bodies. A few mutant cells can be found in the sorus, where they presumably become spores. The segregation of mhcA- mutant cells to the outside of the wild-type aggregation streams argues that the mutant cells are unable to penetrate a mass of adhered, wild-type cells. We hypothesize that mutant cells lacking cortical integrity are unable to generate sufficient protrusive force to break the adhesion of wild-type cells to each other. This would make the mutants incapable of moving through a mass of cells (either mutant or wild type) or of changing shape when adhered to other cells. We propose that mutants lacking myosin II are unable to accomplish morphogenesis because they cannot move correctly in a three-dimensional mass of adhered cells.
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PMID:Three-dimensional localization of wild-type and myosin II mutant cells during morphogenesis of Dictyostelium. 764 74

Conventional myosin has two different light chains bound to the neck region of the molecule. It has been suggested that the light chains contribute to myosin function by providing structural support to the neck region, therefore amplifying the conformational changes in the head following ATP hydrolysis (Rayment et al., 1993). The regulatory light chain is also believed to be important in regulating the actin-activated ATPase and myosin motor function as assayed by an in vitro motility assay (Griffith et al., 1987). Despite extensive in vitro biochemical study, little is known regarding RMLC function and its regulatory role in vivo. To better understand the importance and contribution of RMLC in vivo, we engineered Dictyostelium cell lines with a disrupted RMLC gene. Homologous recombination between the introduced gene disruption vector and the chromosomal RMLC locus (mlcR) resulted in disruption of the RMLC-coding region, leading to cells devoid of both the RMLC transcript and the 18-kD RMLC polypeptide. RMLC-deficient cells failed to divide in suspension, becoming large and multinucleate, and could not complete development following starvation. These results, similar to those from myosin heavy chain mutants (DeLozanne et al., 1987; Manstein et al., 1989), suggest the RMLC subunit is required for normal cytokinesis and cell motility. In contrast to the myosin heavy chain mutants, however, the mlcR cells are able to cap cell surface receptors following concanavilin A treatment. By immunofluorescence microscopy, RMLC null cells exhibited myosin localization patterns different from that of wild-type cells. The myosin localization in RMLC null cells also varied depending upon whether the cells were cultured in suspension or on a solid substrate. In vitro, purified RMLC- myosin assembled to form thick filaments comparable to wild-type myosin, but the filaments then exhibit abnormal disassembly properties. These results indicate that in vivo RMLC is necessary for myosin function.
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PMID:Targeted disruption of the Dictyostelium RMLC gene produces cells defective in cytokinesis and development. 780 58

The complete sequence of the Dictyostelium myosin ID (DMID) heavy chain isoform has been determined from cDNA and genomic clones. Like the DMIB isoform characterized previously, the DMID isoform is up-regulated during starvation-induced chemotactic aggregation, and its 124-kDa heavy chain contains the tail domain sequences that correspond to both the membrane and second actin-binding sites. An antibody that is specific for the DMID isoform was found to stain the actin-rich pseudopods at the leading edge of migrating cells. Protein microsequencing data reveals that the myosin I isoform localized to leading edge pseudopods in a previous study (Fukui, Y., Lynch, T. J., Brzeska, H., and Korn, E. D. (1989) Nature 341, 328-331) was DMIB, indicating that DMID and DMIB also colocalize and that both should influence the dynamics of actin-rich cortical structures. This and other data indicate that the DMID and DMIB isoforms are closely related and are distinct from the DMIA and DMIE isoforms, which possess truncated tail domains and are not up-regulated during chemotactic aggregation. Cells in which the DMID gene was rendered nonfunctional by targeted gene disruption do not show obvious behavioral defects, suggesting that another myosin I isoform(s) (possibly DMIB) might compensate for DMID. Finally, Southern blot data indicate that Dictyostelium may contain as many as nine myosin I isoforms.
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PMID:Sequence, expression pattern, intracellular localization, and targeted disruption of the Dictyostelium myosin ID heavy chain isoform. 832 74


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