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Biomedical subjects

R M Bell

Publications and source records attributed to R M Bell.

At least 199 records · Page 11Linked to original sources
PubMed1984

Asymmetric reconstitution of homogeneous Escherichia coli sn-glycerol-3-phosphate acyltransferase into phospholipid vesicles.

The sn-glycerol-3-phosphate (glycerol-P) acyltransferase of Escherichia coli cytoplasmic membrane was purified in Triton X-100 (Green, P. R., Merrill, A. H., Jr., and Bell, R. M. (1981) J. Biol. Chem. 256, 11151-11159) and incorporated into mixed micelles containing Triton X-100, phosphatidylethanolamine, phosphatidylglycerol, cardiolipin, and beta-octyl glucoside. Enzyme activity was quantitatively reconstituted from the mixed micelle into single-walled phospholipid vesicles by chromatography over Sephadex G-50. Activity coeluted with vesicles of 90-nm average diameter on columns of Sepharose CL-4B and Sephacryl S-1000. These vesicles contained less than 2 Triton X-100 and 5 beta-octyl glucoside molecules/100 phospholipid molecules. Calculations suggested that up to eight 91,260-dalton glycerol-P acyltransferase polypeptides were incorporated per 90-nm vesicle. The pH dependence and apparent Km values for glycerol-P and palmitoyl-CoA of the glycerol-P acyltransferase reconstituted into vesicles were similar to those observed upon reconstitution by mixing of the enzyme in Triton X-100 with a 20-fold molar excess of sonicated phosphatidylethanolamine:phosphatidylglycerol:cardiolipin, 6:1:1. The integrity of vesicles containing glycerol-P acyltransferase was established by trapping 5,5'-dithiobis-(2-nitrobenzoic acid). Chymotrypsin inactivated greater than 95% of the glycerol-P acyltransferase in intact vesicles and cleaved the 91,260-dalton polypeptide into several vesicle-bound and several released peptides, indicating that critical domains of the enzyme are accessible in intact vesicles. Trinitrobenzene sulfonate and 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene caused greater than 90% loss of glycerol-P acyltransferase in vesicles. Disruption of vesicles with Triton X-100 did not reveal significant latent activity. These data strongly suggest that the glycerol-P acyltransferase was reconstituted asymmetrically into the vesicles with its active site facing outward.

Acyltransferases↗
PubMed1984

Transmembrane movement of phosphatidylglycerol and diacylglycerol sulfhydryl analogues.

Transmembrane movement of phospholipids is a fundamental step in the process of biological membrane assembly and intracellular lipid sorting. To facilitate study of transmembrane movement, we have synthesized analogues of phosphatidylglycerol and diacylglycerol in which a sulfhydryl group replaces a hydroxyl group in the polar head group. A rapid, continuous assay for the movement of phospholipids across single-walled lipid vesicles was developed that exploits the reactivity of these analogues toward 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), a nonpenetrating, colorimetric, sulfhydryl reagent. In the reaction of DTNB with vesicles containing phosphatidylthioglycerol, a phosphatidylglycerol analogue, two kinetic phases were seen, which represent the reaction of DTNB with phosphatidylthioglycerol in the outer and inner leaflets of the bilayer. Analysis of the slow second phase indicated that the half-time for phosphatidylthioglycerol transbilayer movement was in excess of 8 days. In a similar experiment using dioleoylthioglycerol, a diacylglycerol analogue, the reaction was complete within 15 s. The large difference in translocation rates between these two lipids indicates that the primary barrier to transmembrane movement is the polar head group and implies that phospholipid translocation events in biological membranes may not be unlike those for molecules similar to the polar head groups alone.

Diglycerides↗
PubMed1984

Glycerolipid synthetic capacity of rat liver peroxisomes.

Investigations on rat liver peroxisomal glycerolipid synthetic capability were performed. Highly purified peroxisomal preparations contained dihydroxyacetone-phosphate acyltransferase, acyldihydroxyacetone-phosphate reductase, and fatty acid-CoA ligase activities. Glycerol-3-phosphate acyltransferase, lysophosphatidic acid acyltransferase, phosphatidic acid phosphatase, diacylglycerol acyltransferase, diacylglycerol cholinephosphotransferase, diacylglycerol ethanolaminephosphotransferase and ethanol acyltransferase activities were low in activity or not detected. These results suggest that the peroxisomes are specialized to contribute to the synthesis of ether-linked glycerolipids. If peroxisomes contribute towards the synthesis of non-ether-linked glycerolipids (i.e., ester-linked) then translocation of acyl glycerophosphatide (acyl dihydroxyacetone phosphatide) from peroxisomes to endoplasmic reticulum would be expected to occur.

Acyltransferases↗
PubMed1984

The triose-phosphate site of homogeneous reconstituted sn-glycerol-3-phosphate acyltransferase of Escherichia coli.

The sn-glycerol-3-phosphate (glycerol-phosphate) acyltransferase of Escherichia coli was purified to near homogeneity and its activity reconstituted with phospholipids (Green, P.R., Merrill, A.M., Jr. and Bell, R.M. (1981) J. Biol. Chem. 256, 11151-11159). The competency of glycerol-P analogues to serve as inhibitors and as substrates was investigated. Dihydroxyacetone-P, ethyleneglycol-P, 1,3-propanediol-P, 3,4-dihydroxybutylphosphonate and DL-glyceraldehyde-3-P were inhibitors of the reconstituted purified glycerol-phosphate acyltransferase. The kinetics of inhibition, while formally of the mixed type, most closely resembled that of a simple competitive inhibition with respect to glycerol-3-P. Inorganic phosphate was also found to be a competitive inhibitor. All of the glycerol-3-P analogues except DL-glyceraldehyde-3-P were substrates. Of these, dihydroxyacetone-P proved to be the best substrate. The secondary hydroxyl was not necessary for activity. Glycerol-phosphate acyltransferase catalyzed the hydrolysis of palmitoyl-CoA in the presence of DL-, but not D-glyceraldehyde-3-P. This suggests that the gem diol of L-glyceraldehyde-3-P may be a substrate, and that the acylated adduct may be unstable. The enzyme was inactivated by phenylglyoxal and butanedione, suggesting that arginine may be at or near the active site.

Acyltransferases↗
PubMed1984

1,2-Diacylglycerols do not potentiate the action of phospholipases A2 and C in human platelets.

1,2-Diacylglycerol has recently been reported to potentiate the ability of phospholipases A and C to hydrolyze phospholipids in a cell-free system. The present study has been undertaken to investigate whether 1,2-diacylglycerol can also perform this function in intact cells using the platelet as a test system. Exogenous 1-oleoyl-2-acetyl-glycerol ( OAG ) and 1,2- didecanoylglycerol , at concentrations sufficient to produce maximal phosphorylation of a 40,000 dalton protein, caused no significant formation of [3H]inositol phosphates and [32P]phosphatidic acid (products of phospholipase C activation) or [14C]arachidonic acid metabolites and lysophosphatidyl[3H]inositol (products of phospholipase A2 activation). These data therefore imply that 1,2-diacylglycerols do not potentiate the actions of phospholipases A2 and C in intact platelets at concentrations that are physiologically relevant.

Blood Platelets↗
PubMed1984

sn-Glycerol-3-phosphate auxotrophy of plsB strains of Escherichia coli: evidence that a second mutation, plsX, is required.

sn-Glycerol-3-phosphate auxotrophs defective in phospholipid synthesis contain a Km-defective sn-glycerol-3-phosphate acyltransferase. Detailed genetic analysis revealed that two mutations were required for the auxotrophic phenotype. One mutation, in the previously described plsB locus (sn-glycerol-3-phosphate acyltransferase structural gene), mapped near min 92 on the Escherichia coli linkage map. Isolation of Tn10 insertions cotransducible with the auxotrophy in phage P1 crosses revealed that a second mutation was required with plsB26 to confer the sn-glycerol-3-phosphate auxotrophic phenotype. This second locus, plsX, mapped between pyrC and purB near min 24 on the E. coli linkage map. Tn10 insertions near plsX allowed detailed mapping of the genetic loci in this region. A clockwise gene order putA pyrC flbA flaL flaT plsX fabD ptsG thiK purB was inferred from results of two- and three-factor crosses. Strains harboring the four possible configurations of the mutant and wild-type plsB and plsX loci were constructed. Isogenic plsB+ plsX+, plsB+ plsX50, and plsB26 plsX+ strains grew equally well on glucose minimal medium without sn-glycerol-3-phosphate. In addition, plsX or plsX+ had no apparent effect on sn-glycerol-3-phosphate acyltransferase activity measured in membrane preparations. The molecular basis for the plsX requirement for conferral of sn-glycerol-3-phosphate auxotrophy in these strains remains to be established.

Acyltransferases↗
PubMed1984

Indications for sealant use in a community-based preventive dentistry program.

Dental caries is a disease that recently has undergone, and may still be undergoing, dramatic changes in distribution of incidence and prevalence. The most recent epidemiologic data available have been reviewed in this paper to illustrate that caries is becoming a disease primarily of pits and fissures, with less differentiation than previously acknowledged between fluoridated and fluoride-deficient areas. The present distribution of caries suggests that prevention may be accomplished more effectively through targeted sealant programs than through currently popular mass preventive programs. Existing information can be used to identify logical target groups for sealant programs, and age specific tooth eruption and caries attack information can be used to design delivery methods. Although the adoption of targeted sealant programs represents a departure from the traditional mass approach to prevention in dental programs, the present-day caries distribution requires that the initiation of such programs be given serious consideration. At the very least program administrators are encouraged to invoke the planning-implementation-evaluation process. Current programs should be evaluated carefully in view of today's disease patterns and the clinical significance of the results achieved. The content, design, and timing of future community-based programs should reflect individualized community diagnosis and the application of new epidemiologic data as well as a careful evaluation of the results achieved by current preventive procedures.

Adolescent↗
PubMed1983

The DNA sequences encoding plsB and dgk loci of Escherichia coli.

We have determined the sequence of a 3865-base pair DNA segment from Escherichia coli containing plsB, the structural gene for the sn-glycerol-3-phosphate acyltransferase, and the dgk locus, believed to encode diglyceride kinase. The 806-amino acid sequence encoded within the longest open reading frame is in agreement with NH2-terminal sequences of the sn-glycerol-3-phosphate acyltransferase (Green, P., Vanaman, T. C., Modrich, P., and Bell, R. M. (1983) J. Biol. Chem. 258, 10862-10866), indicating that this is the structural gene for this protein. Furthermore, an open reading frame encoding a 122-residue polypeptide consistent with the size of diglyceride kinase has been identified and coincides with the position of dgk determined by deletion analysis.

Acetyltransferases↗
PubMed1983

Partial NH2- and COOH-terminal sequence and cyanogen bromide peptide analysis of Escherichia coli sn-glycerol-3-phosphate acyltransferase.

The sn-glycerol-3-phosphate acyltransferase from Escherichia coli, an integral membrane protein whose activity is dependent on phospholipids, was purified to near homogeneity (Green, P. R., Merrill, A. H., Jr., and Bell, R. M., (1981) J. Biol. Chem. 256, 11151-11159). Determination of a partial NH2-terminal sequence and the COOH terminus permitted alignment of the polypeptide on the sequenced sn-glycerol-3-phosphate acyltransferase structural gene (Lightner, V. A., Bell, R. M., and Modrich, P. (1983) J. Biol. Chem. 258, 10856-10861). Processing of the sn-glycerol-3-phosphate acyltransferase is apparently limited to the removal of the NH2-terminal formylmethionine. Thirteen of 27 possible cyanogen bromide peptides predicted from the DNA sequence were purified, characterized, and assigned to their location in the primary structure. Three peptides located at positions throughout the sequence were partially sequenced by automated Edman degradation. The partial sequence analysis of the homogeneous sn-glycerol-3-phosphate acyltransferase is fully in accord with the primary structure inferred from the DNA sequence.

Acyltransferases↗
PubMed1983

Preoperative and postoperative assessment of nutrient intakes in patients who have undergone gastric bypass surgery.

The study of 25 morbidly obese patients who had undergone gastric bypass surgery was undertaken to determine the fat, carbohydrate (CHO), protein, and total caloric intake before and at 1, 3, 6, and 12 months postoperatively. No postoperative complications occurred, and all patients lost weight appropriately. The nutrient intakes were estimated from dietary recall. Dramatic decreases occurred in average total caloric intake from a preoperative value of 3979.4 to 351.6 kcal at 1 month, 471.3 kcal at 3 months, 932.7 kcal at 6 months, and 1091 kcal at 12 months. Fat, CHO, and protein intake decreased equally until 12 months when fat intake had reached a plateau while CHO and protein intake continued to rise. Weight reduction after gastric bypass surgery is related to decreased caloric intake, predominantly in the fat component.

Adult↗
PubMed1983

Technical complications of Roux-en-Y gastrojejunostomy.

The Roux-en-Y gastrojejunostomy has become an increasingly popular technique for gastrointestinal tract reconstruction since it is purported to obviate many of the classic complications of the Billroth II gastrojejunostomy. In a review of over 900 Roux-en-Y gastrojejunostomies, seven patients with complications mimicking those seen with Billroth II reconstruction were identified. These complications included duodenal stump blowout, proximal blind loop or afferent loop syndrome, and bile-reflux gastritis. These complications resulted from technical problems in construction of the Roux-en-Y. Once the complications were diagnosed, they were amenable to operative correction. Recognition of the potential for these complications following Roux-en-Y gastrojejunostomy should aid in early diagnosis and treatment.

Adult↗
PubMed1983

The prophylactic use of antimicrobials in surgery.

During the period August 1976 to June 1982, there were 98 reports of antimicrobial prophylaxis in human surgery that were judged unevaluable. Our review, coupled with that of Chodak and Plaut, identified studies of 126 antibiotic regimens that were considered evaluable and a total of 205 studies considered unevaluable. A decrease in infection rate in antibiotic-treated patients compared to non-antibiotic-treated patients was seen in 120 (95%) of the evaluable regimens. Ninety-nine (79%) of these 120 regimens produced statistically significant reductions in the infection rate (P less than .05, chi 2 analysis). The majority of the antibiotic regimens were tested in procedures that were classified as clean-contaminated. Of the regimens that yielded a statistically significant reduction in infection rate with antimicrobial therapy, in 66 (67%) the agents were used for 24 hours or less. Five regimens were identified in which a higher infection rate occurred in specific patient groups when prophylactic antibiotics were used, but the differences were not statistically significant. In the overwhelming majority of evaluable studies, antibiotics decreased the incidence of surgical infection compared with non-antibiotic groups. The available data also support the effectiveness of short prophylactic antibiotic courses of 24 hours' duration or less. The duration necessary for antibiotic prophylaxis was specifically tested in nine regimens. In all nine, a short course (less than 24 hours) of antibiotic prophylaxis was as effective as longer periods of therapy (24 hours to 5 days) in preventing infection.

Anti-Bacterial Agents↗
PubMed1983

Serum alpha 1-acid glycoprotein and the binding of drugs in obesity.

Although clinically relevant, drug-protein interactions in the morbidly obese population have not been studied thoroughly. The objective of this study was to evaluate serum chemistry profiles and the degree of serum protein binding of propranolol, diazepam and phenytoin in the serum of four female, morbidly obese (greater than 190% of ideal body weight) and eight control female subjects. Serum triglyceride concentrations were higher and high-density lipoproteins were lower in the obese subjects than in the control group. Serum albumin and total protein concentrations in the obese were not different from controls. Unexpectedly, alpha 1-acid glycoprotein concentrations were doubled in the obese subjects (mean obese value 121 mg/100 ml vs 62.9 mg/100 ml for the control subjects). Obese subjects had a mean fraction unbound (fu) for propranolol of 0.086, which was significantly different from the controls (fu = 0.123). The binding of diazepam was decreased slightly in the obese subjects. The binding of phenytoin was similar in both groups. The altered serum chemistry of obesity may play a significant role in the drug management of the obese patient by altering drug-protein interactions.

Adult↗
PubMed1983

The effect of ten and twenty per cent safflower oil emulsion given as thirty to fifty per cent of total calories.

In a prospective study of seven patients undergoing operations, 10 and 20 per cent safflower oil emulsions were found to be safe and effective as a major component of adult parenteral nutrition. Specifically, clinically important adverse effects of the emulsions as monitored by clinical evaluation and screening hematologic and blood chemistry determinations were not identified. Further, an extensive coagulation profile in these patients has failed to identify procoagulant effects of parenteral safflower oil. The optimum dosage of fat for a balanced parenteral diet is not known. Linoleic acid administered as 4 per cent of total calories every other day will treat or prevent essential fatty acid deficiency, and this dosage may be considered a minimum requirement for parenteral fat. The data from this study demonstrate parenteral safflower oil administered as 30 to 50 per cent of total calories is effective in achieving nitrogen balance. The implication is that fat emulsions today allow the use of parenteral diets that match the normal diet consumed orally in terms of the balance of protein, carbohydrate and fat.

Adult↗
PubMed1983

The decline and fall of the jejunoileal bypass.

With the obvious failure of nonoperative means of producing permanent weight reduction in patients with morbid obesity, operative approaches have become popular. In the late 1960's and early 1970's, jejunoileal bypass was shown to produce permanent weight reduction and became the most performed operation. However, as the patients were observed for a long term, many untoward complications became evident. The most serious complication of liver disease and even liver failure with fatalities was observed and has accounted for 91 reported deaths following jejunoileal bypass. Other complications include severe electrolyte imbalance, requiring frequent rehospitalization of the patient; renal calculi which is related to excess oxalate absorption; arthritis which is probably secondary to complement activation of high molecular weight immune complexes formed in response to the absorption of bacterial antigens; cholelithiasis which is related to reduced bile salts; a variety of intestinal difficulties, such as bypass enteritis, and pseudo-obstruction of the colon; osteomalacia and decreased bone mineral content; failure in absorption of some medications and fat-soluble vitamins, and most recently, the possibility of induced carcinoma of the colon. Because of these many complications, it is suggested that the jejunoileal bypass is not an appropriate operation for morbidly obese patients and should be abandoned.

Arthritis↗
PubMed1983

Determining the content of a surgical curriculum.

The purpose of undergraduate surgical education is to prepare the student for both the residency and eventual practice of medicine. To help determine the surgical knowledge and skills that would eventually the useful to the student, we conducted a survey of residents in training, physicians in practice, and surgical educators (department chairpersons and clerkship directors). Members of the Curriculum Committee of the Association for Surgical Education developed a questionnaire in which the respondents were asked to grade the functional importance of 84 areas of knowledge and 46 skills (0 = unnecessary, 3 = proficiency necessary). Using a modified Delphi technique to collect information, we sent the questionnaire to eight medical school graduation classes of 1975 (730 persons) and 1980 (776 persons) and all department chairpersons and/or clerkship directors (179). The results of the survey (46% response) revealed considerable agreement about the importance of certain skills and areas of knowledge, enabling us to rank order skills and knowledge based on mean responses (0.0 to 3.0). Physicians in practice, residents, and educators believed that certain areas of knowledge (e.g., acute abdominal problems, appendicitis, shock, cancer of the breasts) and skills (e.g., history taking and physical examination, gowning, suture removal) were very important (greater than 2.250, while other areas of knowledge (e.g., transplantation, liver abscess, soft tissue sarcomas) and skills (e.g., insertion of Swan-Ganz catheter, abdominal paracentesis, cricothyroidotomy) were less important (less than 1.3). This approach allows us to assign priorities to areas of knowledge and skills when determining curriculum content and to include functional criteria when developing educational objectives.

Attitude of Health Personnel↗