Search PubMed⌕ Search

Biomedical subjects

C Smythe

Publications and source records attributed to C Smythe.

30 records · Page 2Linked to original sources
PubMed1991

Assembly/disassembly of the nuclear envelope membrane: cell cycle-dependent binding of nuclear membrane vesicles to chromatin in vitro.

Dissociation and association of membranes with chromatin at the beginning and end of mitosis are critical in controlling nuclear dynamics during these stages of the cell cycle. Employing purified membrane and cytosolic fractions from Xenopus eggs, a simple assay was developed for the reversible binding of nuclear membrane vesicles to chromatin. We have shown, using phosphatase and kinase inhibitors, that membrane-chromatin association is regulated by a phosphatase/kinase system. In interphase, the balance in this system favors dephosphorylation, possibly of a membrane receptor, which then mediates chromatin binding. At mitosis the membrane receptor is phosphorylated, causing release of chromatin-bound membrane. Purified MPF kinase does not directly cause membranes to dissociate from chromatin. Rather, binding of membranes to chromatin at mitosis appears to be regulated indirectly by MPF through its action on a phosphatase/kinase system that directly modulates the phosphorylation state of a nuclear membrane component.

Animals↗
PubMed1990

Targetting of protein phosphatase 1 to the sarcoplasmic reticulum of rabbit skeletal muscle by a protein that is very similar or identical to the G subunit that directs the enzyme to glycogen.

The amount of protein phosphatase 1 (PP1) activity in rabbit skeletal muscle associated with membranes (predominantly sarcoplasmic reticulum) is similar to that bound to glycogen-protein particles. Membrane-vesicle-associated (sarcovesicular) PP1 can be solubilised with 0.5% Triton X-100 (but not 0.5M NaCl) and is complexed to a protein that is structurally and functionally very similar or identical to the G subunit which targets PP1 to glycogen-protein particles. This conclusion is based on immunoblotting and immunotitration experiments using two different preparations of G-subunit-specific antibodies, binding of Triton-solubilised sarcovesicular enzyme to glycogen, stimulation of phosphorylase phosphatase activity by glycogen, phosphorylation of the same tryptic peptides by cyclic-AMP-dependent protein kinase (A-kinase) and release of catalytic subunit following phosphorylation by A-kinase. Membrane-association is not mediated via glycogen because sarcovesicular PP1 is (1) not released by digestion with alpha-amylase or at dilutions which fully dissociate the glycogen-bound enzyme, and (2) is solubilised by Triton X-100 (whereas glycogen-associated PP1 is not). These findings demonstrate that sarcovesicular PP1 is highly homologous to, or the same as, glycogen-associated PP1G and raises the possibility that a common targetting subunit may direct PP1 to different subcellular locations.

Animals↗
PubMed1990

Further studies on the role of glycogenin in glycogen biosynthesis.

About 90% of the glycogenin in skeletal muscle extracts prepared from fed, 24-h starved or alloxan-diabetic rabbits sedimented at 140,000 x g with the glycogen/sarcovesicular fraction, from which it was released by glycogenolysis, but not by 1% SDS. Glycogenin in the glycogen/sarcovesicular fraction is therefore bound covalently to glycogen, and not associated (covalently or non-covalently) with the sarcoplasmic reticulum. The same proportion of glycogen synthase was also recovered in the glycogen/sarcovesicle fraction, was solubilised by glycogenolysis, and copurified with glycogenin to yield a heterodimer composed of a 1:1 complex between these proteins. Glycogen synthase and glycogenin are therefore present in equimolar amounts in skeletal muscle and there is an average of one glycogen synthase catalytic subunit associated with each molecule of glycogen in vivo. Glycogenin and glycogen synthase released into the muscle cytosol by degradation of glycogen did not form a complex initially, and only 50% reassociation took place after storage for several hours or overnight dialysis. This suggests that the muscle cytosol may contain a factor(s) which regulates glycogen biogenesis by modulating the association of glycogenin and glycogen synthase. Only glycogen synthase that was complexed to glycogenin was capable of elongating the primer formed by incubation of glycogenin with Mn2+ and micromolar concentrations of UDP-glucose, demonstrating the critical importance of this complex for glycogen biogenesis.

Animals↗
PubMed1990

Influence of religion and culture on drinking behaviours: a test of hypotheses between Canada and the USA.

American Roman Catholic and mainstream Protestant students consume more alcohol and have more alcohol abuse problem compared to Canadian students within the same religious groups. Among abstinent oriented Protestants there was no difference in regards to alcohol consumption or problems related to drinking between the countries. For Jews there were mixed results with Americans exhibiting similar consumption rates but reporting more problems related to drinking compared to the Canadians. Among this sample it was concluded that religious norms have a greater influence in cohesive religious groups while cultural norms are more influential among less cohesive groups. The results also support the Canadian 'Mosaic' and American 'Melting Pot' assumption.

Adult↗
PubMed1989

Structural and functional studies on rabbit liver glycogenin.

Glycogenin, the protein primer required for the biogenesis of muscle glycogen, has been isolated from rabbit liver glycogen. The protein comprised 0.0025% of liver glycogen by mass, 200-fold lower than the glycogenin content of muscle glycogen. Structural analyses, including determination of the amino acid sequence surrounding the glucosylated-tyrosine residue, showed identity with muscle glycogenin. Catalytically active liver glycogenin was partially purified and, like the skeletal muscle protein, catalysed an intramolecular, Mn2+- and UDP-Glc-dependent autoglucosylation reaction, forming a primer on which glycogen synthase could act. The results demonstrate that hepatic and muscle glycogenins are almost certainly identical proteins and that liver and skeletal muscle share a common mechanism for the biogenesis of glycogen molecules. The results also indicate that there is about one glycogenin molecule/liver glycogen alpha particle.

Amino Acid Sequence↗
PubMed1988

Glycogenin is the priming glucosyltransferase required for the initiation of glycogen biogenesis in rabbit skeletal muscle.

Purified preparations of glycogen synthase are a complex of two proteins, the catalytic subunit of glycogen synthase and glycogenin, present in a 1:1 molar ratio [J. Pitcher, C. Smythe, D. G. Campbell & P. Cohen (1987) Eur. J. Biochem. 169, 497-502]. This complex has now been found to contain a further glucosyltransferase activity that catalyses the transfer of glucose residues from UDP-Glc to glucosylated-glycogenin. The glucosyltransferase, which is of critical importance in forming the primer required for de novo glycogen biosynthesis, is distinct from glycogen synthase in several ways. It has an absolute requirement for divalent cations, a 1000-fold lower Km for UDP-Glc and its activity is unaffected by incubation with UDP-pyridoxal or exposure to 2 M LiBr, which inactivate glycogen synthase by 95% and 100%, respectively. The priming glucosyltransferase and glycogen synthase activities coelute on Superose 6, and the rate of glycosylation of glycogenin is independent of enzyme concentration, suggesting that the reaction is catalysed intramolecularly by a subunit of the glycogen synthase complex. This component has been identified as glycogenin, following dissociation of the subunits in 2 M LiBr and their separation on Superose 12. The glycosylation of isolated glycogenin reaches a plateau when five additional glucose residues have been added to the protein, and digestion with alpha-amylase indicates that all the glycogenin molecules contain at least one glucosyl residue prior to autoglucosylation. The priming glucosyltransferase activity of glycogenin is unaffected by either glucose 6-phosphate or by phosphorylation of the catalytic subunit of glycogen synthase. The mechanism of primer formation is discussed in the light of the finding that glycogenin is an enzyme that catalyses its own autoglucosylation.

Animals↗
PubMed1988

Isolation and structural analysis of a peptide containing the novel tyrosyl-glucose linkage in glycogenin.

The glucosylation site on glycogenin, the protein primer required for de novo glycogen synthesis, has been identified. The glucose is attached at position C1 in a glycosidic linkage with a unique tyrosine, and the sequence surrounding this residue was found to be: His-Leu-Pro-Phe-Ile-Tyr-Asn-Leu-Ser-Ser-Ile-Ser-Ile-Tyr(Glc)-Ser-Tyr-Leu -Pro- Ala-Phe-Lys. The same tyrosine residue is glycosylated whether glycogenin is isolated as a complex with the catalytic subunit of glycogen synthase, or covalently attached to glycogen. The possibility that insulin and growth factors may enhance glycogen synthesis via stimulation of the priming reaction is discussed.

Amino Acid Sequence↗
PubMed1987

Identification of the 38-kDa subunit of rabbit skeletal muscle glycogen synthase as glycogenin.

Glycogen synthase from rabbit skeletal muscle has been shown to be a complex of two types of subunit which have apparent molecular masses of 86 kDa and 38 kDa and are present in a 1:1 molar ratio. The 38-kDa component was separated from the 86-kDa catalytic subunit by gel filtration in the presence of 2 M LiBr, and a number of chymotryptic peptides were sequenced. This demonstrated that the 38-kDa subunit was glycogenin, the protein that is bound covalently to glycogen and believed to be the 'primer' involved in the initiation of de novo glycogen synthesis.

Amino Acids↗
PubMedDate not supplied

Addictive behavior of older adults.

Very little is known about addictive alcohol use by older people. In the present paper personal effects reasons for drinking (i.e. drinking for the effects of alcohol) and concerns about drinking were used as indicators of addictive drinking behavior among a sample of 826 people aged 65 and older who participated in survey interviews in their homes. The relationship of addictive drinking behavior to frequency of drinking, quantity of drinks per occasion, and depressant drug use was examined. Alcohol use was higher among males and young-old (aged 65-74), while depressant medication use was higher among females and old-old (aged 75+). However, with the exception of use of over-the-counter medications containing codeine (which was significantly higher among current drinkers), no relationship existed between alcohol use and use of depressant medications. Personal effects reasons for drinking and concerns about drinking were related both to alcohol and depressant medication use. Frequency of drinking was associated with higher endorsement of both personal effects and social reasons, whereas volume of alcohol consumption (drinks per drinking day) was associated only with personal effects drinking. In addition, use of depressant medications by drinkers was significantly related to consuming alcohol for personal effects reasons (but unrelated to consuming for social reasons) and with having concerns about one's own drinking. These results suggest that even within the generally low levels of alcohol consumption of older people, addictive-use patterns emerge. In addition, the results confirm the importance of including depressant medication use in evaluating the drinking behavior of older people.

Age Factors↗
PubMedDate not supplied

Information and communication systems for the assistance of carers based on ACTION.

Recent advances in telecommunication technologies allow the design of information and communication systems for people who are caring for others in the home as family members or as professionals in the health or community centres. The present paper analyses and classifies the information flow and maps it to an information life cycle, which governs the design of the deployed hardware, software and the data-structure. This is based on the initial findings of ACTION (assisting carers using telematics interventions to meet older persons' needs) a European Union funded project. The proposed information architecture discusses different designs such as centralized or decentralized Web and Client server solutions. A user interface is developed reflecting the special requirements of the targeted user group, which influences the functionality and design of the software, data architecture and the integrated communication system using video-conferencing. ACTION has engineered a system using plain Web technology based on HTML, extended with JavaScript and ActiveX and a software switch enabling the integration of different types of videoconferencing and other applications providing manufacturer independence.

Adult↗
PubMedDate not supplied

Adaptation to a fish oil diet before inducing sepsis in rats prevents fatty infiltration of the liver.

Hypertriglyceridemia and fatty liver are common lipid abnormalities associated with Gram-negative sepsis. Fish oils have been shown to have beneficial effects in reducing plasma triglycerides (TG). This study was designed to investigate whether fish oils would prevent the elevation of plasma TG and the accumulation of liver lipids during sepsis. One group of rats was fed a 10% menhaden oil diet and the other group was fed a 10% corn oil diet for 14 days. On the 14th day, sepsis was induced by injecting the rats with 8 x 10(7) live Escherichia coli colonies/100 g of body weight and the rats were fasted for 22 hours. The liver composition of total lipids and TG in the septic rats prefed the fish oil was lower than in the septic rats prefed the corn oil. In the rats adapted to the corn oil diet, lipids accumulated in the livers of the septic rats in comparison with the control rats. Hepatocytes isolated from the septic rats adapted to the corn oil diet showed an increased esterification of [1-14C]palmitate into TG and phospholipids than hepatocytes from the control rats. Feeding the fish oil diet instead of the corn oil diet before inducing sepsis reduced TG, cholesterol, and phospholipid synthesis by 58%, 79%, and 71%, respectively. The rise in TG synthesis in the septic rats prefed the corn oil diet was associated with an 89% increase in the activity of phosphatidate phosphohydrolase. There was no significant difference in the activities of glycerol-3-phosphate acyltransferase and phosphatidate phosphohydrolase between control and septic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗