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R Beal

Publications and source records attributed to R Beal.

12 recordsLinked to original sources
PubMed2000

Acute severe pancreatitis and multiple organ failure: total parenteral nutrition is still required in a proportion of patients

AIMS: Enteral nutrition (EN) is increasingly advocated as the favoured means of nutritional support in patients with multiple organ failure resulting from acute severe pancreatitis. In a proportion of patients, however, EN may not be feasible either because of gastrointestinal stasis and high nasogastric aspirates or because of superseding complications of pancreatitis such as fistulation. In these cases total parenteral nutrition (TPN) is indicated. METHODS: Patients with acute severe pancreatitis admitted to the intensive care unit (ICU) were commenced on either nasogastric or, where established, jejunostomy EN. Rates of EN were controlled by protocol and volumes of nasogastric aspirate. TPN was commenced when volumes of EN were persistently inadequate or when this route was contraindicated (e.g. high-volume small bowel fistula). Physiological and outcome data were collected prospectively and included severity of illness scoring (Acute Physiology and Chronic Health Evaluation (APACHE) II), length of stay, duration of EN and TPN, and hospital outcome. RESULTS: Of 69 patients with acute severe pancreatitis, 31 were transferred from other ICUs. The median APACHE II score was 18 (range 4-40) and the overall hospital mortality rate was 39 per cent. Seventeen patients (25 per cent) were managed with EN alone, ten (14 per cent) with TPN alone and 19 (28 per cent) with a combination of both. Twenty-three (33 per cent) did not have any nutritional support during their ICU stay. The mortality rate was worse among patients who received TPN only than in those who had EN (60 versus 24 per cent). CONCLUSIONS: EN is likely to remain the route of choice for nutritional support in the ICU. However, in high-risk patients with acute severe pancreatitis EN may not be feasible and TPN is often required. This may reflect a greater severity of illness.

Journal Article↗
PubMed2000

Role of rhamnolipid biosurfactants in the uptake and mineralization of hexadecane in Pseudomonas aeruginosa.

A study was undertaken to investigate the mechanisms for biosurfactant-enhanced hexadecane uptake into Pseudomonas aeruginosa. Two strains of Ps. aeruginosa were studied, one producing rhamnolipids (PG201) and the other rhamnolipid deficient (UO299). Rhamnolipids produced by PG201 acted to increase the solubility of n-hexadecane in the culture medium (from 1.84 to 22.76 microg l(-1). Rates of(l4)C-n-hexadecane uptake and mineralization were higher in PG201 than in UO299. However, the degree of difference was lower than expected. Additional studies were carried out on the cell surface properties of the two strains. During growth on n-hexadecane, the cell surface hydrophobicity of both PG201 (50.5%) and UO299 (33.7%) increased compared with that observed in water-soluble growth substrates (7-8%). Studies were also carried out to ascertain any energy requirements for the transport of n-hexadecane into Ps. aeruginosa cells. The addition of CCCP (an inhibitor of cytochrome oxidase which thereby blocks oxidative phosphorylation) at a range of concentrations caused a marked decrease in n-hexadecane uptake, indicating that n-hexadecane uptake in Ps. aeruginosa is an energy-dependent process. These studies support the hypothesis of alkane transport into microbial cells by direct contact with larger alkane droplets and by pseudosolubilization. Also, it appears that both mechanisms occur simultaneously.

Alkanes↗
PubMed1997

Inhibition of the 26 S proteasome by polyubiquitin chains synthesized to have defined lengths.

Ubiquitin is a covalent signal that targets cellular proteins to the 26 S proteasome. Multiple ubiquitins can be ligated together through the formation of isopeptide bonds between Lys48 and Gly76 of successive ubiquitins. Such a polyubiquitin chain constitutes a highly effective proteolytic targeting signal, but its mode of interaction with the proteasome is not well understood. Experiments to address this issue have been limited by difficulties in preparing useful quantities of polyubiquitin chains of uniform length. We report a simple method for large scale synthesis of Lys48-linked polyubiquitin chains of defined length. In the first round of synthesis, two ubiquitin derivatives (K48C-ubiquitin and Asp77-ubiquitin) were used as substrates for the well characterized ubiquitin-conjugating enzyme E2-25K. Diubiquitin blocked at the nascent proximal and distal chain termini was obtained in quantitative yield. Appropriately deblocked chains were then combined to synthesize higher order chains (tetramer and octamer in the present study). Deblocking was achieved either enzymatically (proximal terminus) or by chemical alkylation (distal terminus). Chains synthesized by this method were used to obtain the first quantitative information concerning the influence of polyubiquitin chain length on binding to the 26 S proteasome; this was done through comparison of different length (unanchored) polyubiquitin chains as inhibitors of ubiquitin-conjugate degradation. K0.5 was found to decrease approximately 90-fold, from 430 to 4.8 microM, as the chain was lengthened from two to eight ubiquitins. The implications of these results for the molecular basis of chain recognition are discussed.

Alkylation↗
PubMed1996

Surface hydrophobic residues of multiubiquitin chains essential for proteolytic targeting.

Ubiquitin conjugation is a signal for degradation of eukaryotic proteins by the 26S protease. Conjugation of a homopolymeric multiubiquitin chain to a substrate lysine residue results in 10-fold faster degradation than does conjugation of monoubiquitin, but the molecular basis of enhanced targeting by chains is unknown. We show that ubiquitin residues L8, I44, and V70 are critical for targeting. Mutation of pairs of these residues to alanine had little effect on attachment of ubiquitin to substrates but severely inhibited degradation of the resulting conjugates. The same mutations blocked the binding of chains to a specific subunit (S5a) of the regulatory complex of the 26S protease. The side chains implicated in this binding--L8, I44, and V70--form repeating patches on the chain surface. Thus, hydrophobic interactions between these patches and S5a apparently contribute to enhanced proteolytic targeting by multiubiquitin chains.

Biopolymers↗
PubMed1994

Substrate properties of site-specific mutant ubiquitin protein (G76A) reveal unexpected mechanistic features of ubiquitin-activating enzyme (E1).

Ubiquitin-mediated proteolysis proceeds via the formation and degradation of ubiquitin-protein conjugates. Ubiquitin (Ub)-activating enzyme (E1) catalyzes the first, MgATP-dependent step in the conjugative reaction sequence. With wild type ubiquitin, the product of the E1 reaction is a ternary complex (E1-Ub-AMP-Ub) containing one thiol-linked ubiquitin (via the Ub COOH terminus, Gly-76) and one tightly bound ubiquitin adenylate. The thiol-linked ubiquitin is subsequently transferred to the thiol of a ubiquitin-conjugating enzyme (E2 protein); the latter adduct is the proximal donor of ubiquitin to the target protein. A mutant ubiquitin, bearing a Gly to Ala substitution at the COOH terminus (G76A-ubiquitin), was characterized as a substrate for E1. G76A-ubiquitin 1) supported PPi-ATP exchange poorly (500-fold decrease in kcat/K(m); 2) did not produce detectable AMP-Ub with native E1; 3) produced stoichiometric AMP-Ub with thiol-blocked E1; 4) gave a stoichiometric burst of ATP consumption (1 mol/mol E1) with either native or thiol-blocked E1; 5) supported E1-ubiquitin thiol ester formation with native E1; 6) supported several downstream reactions of the proteolytic pathway at approximately 20% of the rate of wild type ubiquitin. These results indicate that G76A-ubiquitin gives a binary E1 thiol ester complex with native E1, due to the failure of the E1-ubiquitin thiol ester to undergo another round of adenylate synthesis; thus AMP-Ub is detected only if adenylate to thiol transfer is prevented by alkylating E1. The inability of G76A-ubiquitin to support ternary complex formation has implications for E1 active site structure. In other experiments, occupancy of the nucleotide/adenylate site of E1, by either MgATP or AMP-Ub, was found to stimulate ubiquitin transthiolation between E1 and E2 proteins. The intermediacy of ubiquitin adenylate thus provides a previously unrecognized catalytic advantage in the E1 mechanism.

Adenosine Monophosphate↗
PubMed1976

Iron and blood donation. Evaluation of a kit method for routine use in a blood transfusion service.

Manifest iron-deficiency anaemia is preceded by a latent stage in which normal haemoglobin levels coexist with low serum iron levels. Regular blood donation involves the removal of significant amounts of iron, and in susceptible donors, may aggravate iron deficiency. It is important for a blood transfusion service to be able to identify these susceptible donors. A commercial kit for the determination of serum iron levels was evaluated and found suitable for introduction as a routine screening test for a transfusion service. A survey of serum iron levels of 200 blood donors showed that 12 1/2% had levels below the normal reference range.

Anemia, Hypochromic↗