The folding and assembly of the dodecameric type II dehydroquinases

The dodecameric type II dehydroquinases (DHQases) have an unusual quaternary structure in which four trimeric units are arranged with cubic 23 symmetry. The unfolding and refolding behaviour of the enzymes from Streptomyces coelicolor and Mycobacterium tuberculosis have been studied. Gel-permeation studies show that, at low concentrations (0.5 M) of guanidinium chloride (GdmCl), both enzymes dissociate into trimeric units, with little or no change in the secondary or tertiary structure and with a 15% loss (S. coelicolor) or a 55% increase (M. tuberculosis) in activity. At higher concentrations of GdmCl, both enzymes undergo sharp unfolding transitions over narrow ranges of the denaturant concentration, consistent with co-operative unfolding of the subunits. When the concentration of GdmCl is lowered by dilution from 6 M to 0.55 M, the enzyme from S. coelicolor refolds in an efficient manner to form trimeric units, with more than 75% regain of activity. Using a similar approach the M. tuberculosis enzyme regains less than 35% activity. From the time courses of the changes in CD, fluorescence and activity of the S. coelicolor enzyme, an outline model for the refolding of the enzyme has been proposed. The model involves a rapid refolding event in which approximately half the secondary structure is regained. A slower folding process follows within the monomer, resulting in acquisition of the full secondary structure. The major changes in fluorescence occur in a second-order process which involves the association of two folded monomers. Regain of activity is dependent on a further associative event, showing that the minimum active unit must be at least trimeric. Reassembly of the dodecameric S. coelicolor enzyme and essentially complete regain of activity can be accomplished if the denatured enzyme is dialysed extensively to remove GdmCl. These results are discussed in terms of the recently solved X-ray structures of type II DHQases from these sources.

Site-directed mutagenesis of proline 204 in the 'hinge' region of yeast phosphoglycerate kinase

Site-specific mutants have been produced in order to investigate the role of proline 204 in the 'hinge' region of yeast phosphoglycerate kinase (PGK). This totally conserved proline has been shown to be the only cis-proline in the high resolution crystal structures of yeast, B. stearothermophilus, T. brucei and T. maritima PGK, and may therefore have a role in the independent folding of the two domains or in the 'hinge' bending of the molecule during catalysis. The residue was replaced by a histidine (Pro204His) and a phenylalanine (Pro204Phe), and the resulting proteins characterised by differential scanning calorimetry (DSC), circular dichroism (CD), tryptophan fluorescence emission and kinetic analysis. Although the secondary and tertiary structure of the Pro204His protein is generally similar to that of the wild-type enzyme as assessed by CD, the enzyme is less stable to heat and guanidinium chloride denaturation than the wild-type. In the denaturation experiments two transitions were observed for both the wild-type and the Pro204His mutant, as have been previously reported for yeast PGK [Missiakas, D., Betton, J.M., Minard, P. & Yon, J.M. (1990) Biochemistry 29, 8683-8689]. The first transition is accompanied by an increase in fluorescence intensity leading to a hyperfluorescent state, followed by the second, corresponding to a decrease in fluorescence intensity. However, for the Pro204His mutant, the first transition proceeded at lower concentrations of guanidinium chloride and the second transition proceeded to the same extent as for the wild-type protein, suggesting that sequence-distant interactions are more rapidly disrupted in this mutant enzyme than in the wild-type enzyme, while sequence-local interactions are disrupted in a similar way. The Michaelis constants (K(m)) for both 3-phospho-D-glycerate and ATP are increased only by three or fourfold, which confirms that, as expected, the substrate binding sites are largely unaffected by the mutation. However, the turnover and efficiency of the Pro204His mutant is severely impaired, indicating that the mechanism of 'hinge' bending is hindered. The Pro204Phe enzyme was shown to be significantly less well folded than the wild-type and Pro204His enzymes, with considerable loss of both secondary and tertiary structure. It is proposed that the proline residue at 204 in the 'hinge' region of PGK plays a role in the stability and catalytic mechanism of the enzyme.

The role of the C-terminal region in phosphoglycerate mutase

Removal of the C-terminal seven residues from phosphoglycerate mutase from Saccharomyces cerevisiae by limited proteolysis is associated with loss of mutase activity, but no change in phosphatase activity. The presence of the cofactor 2, 3-bisphosphoglycerate, or of the cofactor and substrate 3-phosphoglycerate together, confers protection against proteolysis. The substrate alone offers no protection. Replacement of either or both of the two lysines at the C-terminus by glycines has only limited effects on the kinetic properties of phosphoglycerate mutase, indicating that these residues are unlikely to be involved in crucial electrostatic interactions with the substrate, intermediate or product in the reaction. However, the double-mutant form of the enzyme is more sensitive to proteolysis and is no longer protected against proteolysis by the presence of cofactor. The proteolysed wild-type and two of the mutated forms of the enzyme show a reduced response to 2-phosphoglycollate, which enhances the instability of the phospho form of the native enzyme. The phosphoglycerate mutase from Schizosaccharomyces pombe, which lacks the analogous C-terminal tail, has an inherently lower mutase activity and is also less responsive to stimulation by 2-phosphoglycollate. It is proposed that the C-terminal region of phosphoglycerate mutase helps to maintain the enzyme in its active phosphorylated form and assists in the retention of the bisphosphoglycerate intermediate at the active site. However, its role seems not to be to contribute directly to ligand binding, but rather to exert indirect effects on the transfer of the phospho group between substrate, enzyme, intermediate and product.

The herpes simplex virus triplex protein, VP23, exists as a molten globule

Two proteins, VP19C (50,260 Da) and VP23 (34,268 Da), make up the triplexes which connect adjacent hexons and pentons in the herpes simplex virus type 1 capsid. VP23 was expressed in Escherichia coli and purified to homogeneity by Ni-agarose affinity chromatography. In vitro capsid assembly experiments demonstrated that the purified protein was functionally active. Its physical status was examined by differential scanning calorimetry, ultracentrifugation, size exclusion chromatography, circular dichroism, fluorescence spectroscopy, and 8-anilino-1-naphthalene sulfonate binding studies. These studies established that the bacterially expressed VP23 exhibits properties consistent with its being in a partially folded, molten globule state. We propose that the molten globule represents a functionally relevant intermediate which is necessary to allow VP23 to undergo interaction with VP19C in the process of capsid assembly.

Flight controller alertness and performance during spaceflight shiftwork operations

Decreased alertness and performance associated with fatigue, sleep loss, and circadian disruption are issues faced by a diverse range of shiftwork operations personnel. During Space Transportation System (STS) operations, Mission Operations Directorate (MOD) personnel provide 24-hr. coverage of critical tasks. A joint NASA Johnson Space Center and NASA Ames Research Center project was undertaken to examine these issues in flight controllers during MOD shiftwork operations. An initial operational test of procedures and measures was conducted during the STS-53 mission in December 1992. The study measures included a Background Questionnaire, a subjective daily logbook completed on a 24-hour basis (to report sleep patterns, work periods, etc.), and an 8 minute performance and mood test battery administered at the beginning, middle, and end of each shift period. Seventeen flight controllers representing the 3 Orbit shifts participated. The initial results clearly support the need for further data collection during other STS missions to document baseline levels of alertness and performance during MOD shiftwork operations. Countermeasure strategies specific to the MOD environment are being developed to minimize the adverse effects of fatigue, sleep loss, and circadian disruption engendered by shiftwork operations. These issues are especially pertinent for the night shift operations and the acute phase advance required for the transition of day shift personnel into the night for shuttle launch. Implementation and evaluation of the countermeasure strategies to maximize alertness and performance is planned. As STS missions extend to further EDO (extended duration orbiters), and timelines and planning for 24-hour Space Station operations continue, alertness and performance issues related to sleep and circadian disruption will remain highly relevant in the MOD environment.

A 3-month, double-blind, controlled trial of feeding with sucrose polyester in human volunteers

Sucrose polyester (SPE) is a tasteless, odourless substance which reduces plasma cholesterol concentrations and may therefore be valuable as a fat substitute in human foodstuffs. It has recently been approved for use in snack foods by the United States Federal Drug Administration. The current study was designed to investigate its effects on gastrointestinal physiology and nutrient absorption in human subjects. A 6-month (2 x 3-month periods) double-blind, placebo-controlled, randomized, cross-over trial of SPE and control fat was performed in healthy free-living volunteers. Subjects consumed 20-40 g of SPE daily (mean 26.8 (SE 6.8) g) which reduced the intake of total and saturated fat but had no effect on energy intake or body weight. Plasma cholesterol and triacylglycerols were reduced. The frequency of bowel movements and their urgency were increased and anal leakage occurred in 7.2% of subjects. Abdominal pain was more frequent in subjects receiving SPE and was significantly greater than in the control group after 8 weeks feeding. The plasma concentrations of vitamin E and six carotenoids were significantly reduced. Routine haematology and biochemistry, other vitamins, intestinal biopsies, bile-salt retention, rectal prostaglandins, fractional Ca absorption and aminopyrine metabolism were unaffected. The ingestion of foods containing 20-40 g SPE daily provoked significant gastrointestinal problems. This intake is greater than that to be expected from the use of SPE in savoury snack foods, for which it has been approved by the United States Federal Drug Administration. However, the favourable effects on lipid profiles must be balanced against the reduction in the concentrations of vitamins and carotenoids, as these compounds may have beneficial effects on health through protection from free-radical oxidative stress.

A model for cytoplasmic rheology consistent with magnetic twisting cytometry

Magnetic twisting cytometry is gaining wide applicability as a tool for the investigation of the rheological properties of cells and the mechanical properties of receptor-cytoskeletal interactions. Current technology involves the application and release of magnetically induced torques on small magnetic particles bound to or inside cells, with measurements of the resulting angular rotation of the particles. The properties of purely elastic or purely viscous materials can be determined by the angular strain and strain rate, respectively. However, the cytoskeleton and its linkage to cell surface receptors display elastic, viscous, and even plastic deformation, and the simultaneous characterization of these properties using only elastic or viscous models is internally inconsistent. Data interpretation is complicated by the fact that in current technology, the applied torques are not constant in time, but decrease as the particles rotate. This paper describes an internally consistent model consisting of a parallel viscoelastic element in series with a parallel viscoelastic element, and one approach to quantitative parameter evaluation. The unified model reproduces all essential features seen in data obtained from a wide variety of cell populations, and contains the pure elastic, viscoelastic, and viscous cases as subsets.

Structural plasticity of the feline leukaemia virus fusion peptide: a circular dichroism study

The secondary structure of the feline leukaemia virus (FeLV) fusion peptide was investigated using circular dichroism (CD). Our results show that this peptide can readily flip between random, alpha-helical and beta-sheet conformations, depending upon its environment. The CD spectrum changes from one characteristic of random coil to predominantly beta-sheet type, and finally to that showing the characteristics of alpha-helical structure on moving from an aqueous solvent, through several increasingly hydrophobic systems, to a highly hydrophobic solvent. Electron microscopy confirmed the presence of beta structure. We propose that the structural plasticity demonstrated here is crucial to the ability of the fusion peptide to perturb lipid bilayers, and thus promote membrane fusion.

Characterization and immunogenicity of Salmonella typhimurium SL1344 and UK-1 delta crp and delta cdt deletion mutants

S. typhimurium SL1344 and UK-1 mutants with deletions of the crp (cyclic AMP receptor protein) and cdt (colonization of deep tissues) genes have been constructed and characterized, and their levels of virulence and immunogenicity have been determined for BALB/c mice. All Crp- Cdt- and Crp+ Cdt- mutants were avirulent, as mice survived oral doses of 10(9) cells without illness. All the mutants colonized the gut-associated lymphoid tissue efficiently, but capacities to colonize deeper tissues, such as those of the spleen and liver, and blood were significantly reduced for the Crp- Cdt- and Crp+ Cdt- mutants compared with the Crp- Cdt+ mutant and the wild-type parent strain. The Crp- Cdt- and Crp+ Cdt- SL1344 strains induced complete protection, as all mice immunized with the mutants survived challenge with approximately 10(4) times the 50% lethal dose of the wild-type SL1344 strain. The Crp- UK-1 strain was least attenuated yet induced the highest level of protective immunity against challenge with the wild-type UK-1 strain. The Crp+ Cdt- and Crp- Cdt- strains, although totally attenuated, differed in immunogenicity to challenge with the highly virulent UK-1 parent, with the apparently hyperattenuated Crp- Cdt- strain inducing a lower level of protective immunity than the Crp+ Cdt- strain. Nevertheless, these UK-1 Crp- Cdt- and Crp+ Cdt- strains induced complete protective immunity to challenge with the less-virulent SL1344 wild-type strain. Taken collectively, the results indicate that the attenuation of a highly virulent S. typhimurium strain can yield a vaccine that induces excellent protective immunity to challenge with less-virulent S. typhimurium strains.

The Ov20 protein of the parasitic nematode Onchocerca volvulus. A structurally novel class of small helix-rich retinol-binding proteins

Ov20 is a major antigen of the parasitic nematode Onchocerca volvulus, the causative agent of river blindness in humans, and the protein is secreted into the tissue occupied by the parasite. DNA encoding Ov20 was isolated, and the protein was expressed in Escherichia coli. Fluorescence-based ligand binding assays show that the protein contains a high affinity binding site for retinol, fluorescent fatty acids (11-((5-dimethylaminonaphthalene-1-sulfonyl)amino)undecanoic acid, dansyl-DL-alpha-aminocaprylic acid, and parinaric acid) and, by competition, oleic and arachidonic acids, but not cholesterol. The fluorescence emission of dansylated fatty acids is significantly blue-shifted upon binding in comparison to similarly sized beta-sheet-rich mammalian retinol- and fatty acid-binding proteins. Secondary structure prediction algorithms indicate that a alpha-helix predominates in Ov20, possibly in a coiled coil motif, with no evidence of beta structures, and this was confirmed by circular dichroism. The protein is highly stable in solution, requiring temperatures in excess of 90 degrees C or high denaturant concentrations for unfolding. Ov20 therefore represents a novel class of small retinol-binding protein, which appears to be confined to nematodes. The retinol binding activity of Ov20 could possibly contribute to the eye defects associated with onchocerciasis and, because there is no counterpart in mammals, represents a strategic target for chemotherapy.

Measurement of elastic properties of Xenopus oocytes

Elastic properties of Xenopus oocytes were examined by measuring intracellular pressure (Pic) and cell volume (Vc) in cells undergoing osmotic swelling. Pic was measured by micropuncture, using the servo-null technique. Vc was obtained by analyzing images acquired from a microscope having a video camera attachment. During osmotic swelling, Pic increased from 61 +/- 17 to 500 +/- 59 Pa (mean +/- SE), but the relationship with volume was not linear. In cells that underwent sequential swelling and shrinking, Pic was always lower on shrinking and the cells showed hysteresis. Cells with vitelline envelope (VE) removed had Pic-Vc curves similar in shape to those of intact cells; however, Pic values were significantly lower. Specific elastance[delta Pic/(delta Vc/Vc)] was reduced by removal of the VE. The data indicate that oocytes are weakly elastic and that a large part of their resistance to expansion resides in the VE.

Base rate data on the abnormality of subtest scatter for WAIS-R short-forms

Tables are presented which permit clinicians to determine the abnormality of a WAIS-R subtest profile when one of nine different short-forms has been administered. The tables record the discrepancy, between each subtest and the individual's mean subtest score, which must be exceeded to occur in less than 15 per cent or 5 per cent of the healthy population. Two tables are provided; the first uses a statistical formula developed by Silverstein (1984a) to estimate the discrepancies from the US standardization sample. The second presents empirically derived discrepancies based on a sample of 326 healthy individuals which was representative of the adult UK population in terms of age, sex and social class distributions. The UK sample was also used to generate base rate data on the cumulative number of abnormal subtest deviations exhibited by healthy individuals.

Surface activity properties of cysteine-substituted C-terminal melittin analogues

In order to extend our knowledge of factors important in the surface activity of melittin, cysteine was substituted for lysine-21 and lysine-21/glutamine-25 in a pair of synthetic peptide analogues. The first of these changes resulted in only modest effects on secondary structure (determined in 50% trifluoroethanol), emulsification and surface tension properties. Introduction of a second cysteine greatly reduced both the rate of surface tension decay and the equilibrium surface tension attained, although secondary structure (determined in 50% trifluoroethanol) was only slightly affected by this modification. This latter peptide completely lacked emulsification and haemolytic properties and was found to oligomerise readily due to the formation of intermolecular, disulphide bridges. These results indicate that oligomerisation abolishes surface activity in melittin.

Safety and immunogenicity in humans of an attenuated Salmonella typhi vaccine vector strain expressing plasmid-encoded hepatitis B antigens stabilized by the Asd-balanced lethal vector system

Attenuated Salmonella typhi organisms which express genes encoding protective antigens of other pathogens have been developed for use as experimental oral vaccines. A delta asd S. typhi strain attenuated by deletions in cya, crp, and cdt which contains hepatitis B core (HBc) and pre-S genes encoded on an Asd+ pBR-based plasmid vector was constructed. Healthy adult volunteers ingested a single dose of 5 x 10(5) to 5 x 10(8) CFU of strain chi4073 (delta cya delta crp delta cdt S. typhi Ty2), 6 x 10(7) or 1 x 10(9) CFU of strain chi4632(pYA3149), a further derivative of chi4073 deleted in asd and containing the Asd+ vector without the HBc-pre-S fusion, or 3 x 10(7) or 7 x 10(8) CFU of strain X4632(pYA3167), a derivative containing the vector with the HBc-pre-S fusion. Chi4073 was generally well tolerated by 22 volunteers. No volunteer had fever or positive blood cultures; 4 of 22 volunteers shed vaccine organisms in the stool in the first 48 h only. Two of 18 volunteers who received one of the plasmid-containing derivatives of chi4073 developed low-grade fevers on day 10 or 12 after ingestion. One of these volunteers had positive blood cultures on days 7 and 8. Seven of these 18 volunteers had vaccine organisms detected in their stools in the first 48 h only. Most volunteers developed S. typhi-specific serum responses and developed S. typhi-specific antibody-secreting cells. However, no volunteer developed serum antibody to hepatitis pre-S or pre-S-specific antibody-secreting cells. Although the parent strain chi4073 was well tolerated, induced immunoglobulin G seroconversion to S. typhi lipopolysaccharide in 80 to 100% of vaccinees and stimulated specific IgA-secreting lymphocytes in 80 to 100% of vaccinees given a single oral dose of 2 x 10(7) and 5 x 10(8) CFU, chi4073 derivatives containing the Asd+ vector with and without sequences encoding the HBc-pre-S fusion caused occasional febrile reactions at high doses and did not stimulate detectable immune responses to hepatitis B antigens.

Association between liver transplantation for Langerhans cell histiocytosis, rejection, and development of posttransplant lymphoproliferative disease in children

OBJECTIVE

Langerhans cell histiocytosis (LCH) is an unusual indication for orthotopic liver transplantation in children. Data from limited case reports suggest that orthotopic liver transplantation for LCH is associated with excellent survival rates and a low incidence of disease recurrence. However, in our experience, children who have transplantation for LCH appeared to experience a high incidence of refractory rejection and posttransplant lymphoproliferative disease (PTLD).

STUDY DESIGN

Data from 398 liver transplants performed in 298 children younger than 16 years of age were reviewed to determine the presence of risk factors for PTLD in patients with LCH and other causes of liver failure.

RESULTS

The incidence of PTLD was significantly higher in children who received transplants for LCH compared with all indications (p < 0.001) and specific indications that were associated with the development of PTLD (p < 0.002). Among patients in whom PTLD developed, there was no significant difference in the incidence of primary Epstein-Barr virus infections in patients who receive transplantation for LCH (4/4, 100%) versus all other indications (12/14, 86%). Children who had transplantation for LCH were older than those who had transplantation for other indications (LCH median age 3.1 years, other indications 1 year). The incidence of rejection, especially refractory rejection, was greater in patients who had transplantation for LCH (100% and 50%, respectively) compared with those who had transplantation for other indications (70% and 10%, p < 0.02 for refractory rejection).

CONCLUSIONS

Patients who had transplantation for liver disease related to LCH experienced a 67% long-term survival (median follow up 5.8 years, range 2.1 to 7.5 years). Recurrent LCH occurred in only 33% of patients and was easily managed. However, PTLD developed in two thirds of these patients, perhaps in part because of the high incidence of refractory rejection. This series therefore demonstrates an association between a primary disease process and the development of PTLD. Although the data indicate that children with LCH-induced liver failure benefit from transplantation, special care must be exercised in screening for and preemptive treatment of PTLD.

Synthetic, structural and biological studies of the ubiquitin system: synthesis and crystal structure of an analogue containing unnatural amino acids

Ubiquitin is a 76-amino acid protein involved in the targeting for destruction of proteins in the cell. The protein can readily be synthesized chemically affording an extra dimension to studies of protein stability. Ubiquitin with various modifications to the hydrophobic core has been synthesized. In particular, two core amino acids have been replaced by aminobutyric acid (Val-26) and norvaline (for Ile-30) and the product crystallized. The refined crystal structure shows an overall contraction of the molecule and the side chain of Nva-30 rotates relative to Ile-30. However, the side chain rotation is not sufficient to compensate for the effect of the loss of the methyl group and hence a small cavity is introduced into the structure, which decreases the stability of the protein. The biological behaviour of the modified protein is unaltered. The observed changes in stability are of the magnitude expected for the removal of methyl groups from the hydrophobic core of a protein. Interestingly, the effect appears to be independent of the position of the removed methyl group. The intact structure, but not its stability, is important for recognition by the biological conjugating system.

Patterns of hepatic and splenic colonization by an attenuated strain of Salmonella typhimurium containing the gene for human interleukin-2: a novel anti-tumor agent

Currently, there is no effective treatment for unresectable hepatic malignancies. Salmonella sp. are known to naturally track to the liver during active infection. A live biological vector was developed for delivery of Interleukin-2 (IL-2) to the liver for anti-tumor purposes. The avirulent and highly immunogenic c4550 strain of Salmonella typhimurium was used to express the IL-2 protein [renamed c4550(pIL-2)]. We have previously demonstrated that the c4550(pIL-2) produces biologically active IL-2 (up to 46.2 IU/ml) and that a single gavage feeding of 10(7) colony forming units (cfu) of c4550(pIL-2) significantly reduced the number of hepatic metastases when compared to animals fed salmonella lacking the IL-2 gene or non-treated controls. The goal of the current studies was to determine the pattern of splenic and hepatic colonization of Salmonella-IL2. Hepatic and splenic colonization was determined following administration of 10(7) cfu of c4550(pIL-2) and c4550(pYA292) via a single gavage feeding to C57BL/6 mice. Five experiments of antibiotic regimen administration were conducted where splenic and hepatic homogenates were cultured after 14 days of parenteral and/or oral antibiotics. The natural history of hepatic and splenic colonization was also determined for animals without antibiotic treatment. Despite administration of various antibiotic regimens using different routes, eradication of salmonella with and without IL-2 was not achieved. Salmonella, however, was not cultured from hepatic and splenic tissue at 4 months after a single gavage feeding of salmonella with no specific treatment. In conclusion, oral administration of c4550(pIL-2) may represent a novel form of in vivo biotherapy for unresectable hepatic malignancies. Antibiotics do not accelerate eradication of this bacteria and it appears that c4550(pIL-2) follows the natural pathophysiological of salmonella infection in which eradication from the splenic and hepatic tissue occurs over a period of 2-4 months.

Antitumor mechanisms of attenuated Salmonella typhimurium containing the gene for human interleukin-2: a novel antitumor agent?

Currently, there is no long-term effective treatment for unresectable hepatic malignancies. Salmonella species are known to naturally track to the liver during active infection. To develop a biological vector for delivery of interleukin-2 (IL-2) to the liver for antitumor purposes, the thi 4550 attenuated strain of Salmonella typhimurium was used as a vector for IL-2. The gene for human IL-2 was cloned into plasmid pYA292 and inserted into the attenuated S typhimurium and renamed (thi 4550(pIL-2)]. MCA-38 murine adenocarcinoma cells were injected intrasplenically into C57BL/6 mice to produce hepatic metastases that were subsequently enumerated after 12 days. We previously have demonstrated that the thi 4550(pIL-2) produces biologically active IL-2 and that a single gavage feeding of 10(7) thi 4550(pIL-2) significantly reduced the number of hepatic metastases when compared with animals fed salmonella lacking the IL-2 gene or nontreated controls. The aims of the current studies were to determine which host effector cell populations were responsible for the antitumor effect seen with thi 4550(pIL-2) by depletion of natural killer (NK), cytotoxic T lymphocytes (CD8+), T helper (CD4+) cells, and Kupffer cells. Multiple experiments were conducted for each host effector cell population depleted. We found a consistent reduction in the mean number of hepatic metastases in animals fed thi 4550(pIL-2) (55.6 metastases; n = 54) when compared with controls (162.3 metastases; n = 53) (P < .0001). Depletion of NK cells and CD8+ T cells significantly inhibited the antitumor effect of thi 4550(pIL-2) (analysis of variance [ANOVA], P < .01). Elimination of CD4+ T cells and Kupffer cells had no significant impact on the antitumor effect of thi 4550(pIL-2) (ANOVA, P value was not significant). Salmonella IL-2 may represent a novel form of in vivo biotherapy for unresectable hepatic malignancies that employs the oral route of administration. Furthermore, both NK cells or CD8+ cells are required for the antitumor effect seen while CD4+ T cells and Kupffer cells do not appear to be as essential.

Glucose modification of human serum albumin: a structural study

Structural changes associated with the exposure of human serum albumin (HSA) to glucose with or without the presence of Cu (II) have been characterized using a bank of methods for structural analysis including circular dichroism (CD), amino acid analysis (AAA), fluorescence measurements, SDS-PAGE, and boronate binding (which is a measure of Amadori product formation). We show that in the short-term (10 d) incubation mixtures, HSA is resistant to Cu (II)-mediated oxidative damage and that the early products of glycation of HSA had minimal effects on the folded structure. Amino acid analysis showed that there was no formation of advanced glycation endproducts (AGE), which can be measured by loss of lysine. This remained the case in longer term incubation of HSA (56 d) in the hyperglycemic concentration range (5-25 mM glucose) despite increased levels of Amadori product (60% boronate binding) and the formation of glycophore (Excitation 350, Emission 425). At high, nonphysiological concentrations (100 mM and 500 mM) of glucose, glycophore formation increased and 3 and 11 mol Lysine-glucose adduct/mol HSA were converted to AGE, respectively. This was accompanied by increased damage to tryptophan and protein-protein crosslinking but only minor tertiary structural change. In the presence of Cu (II), however, AGE formation was accompanied by extensive damage to histidine and tryptophan side chains, main chain fragmentation, and loss of both secondary and tertiary structure. Thus, changes in structure appear to be the result of oxidation as opposed to glycation, per se.

The need for pediatric-specific triage criteria: results from the Florida Trauma Triage Study

OBJECTIVE

The objective of the Florida Trauma Triage Study was to assess the performance of state-adopted field triage criteria. The study addressed three specific age groups: pediatric (age < 15 years), adult (age 15-54 years), and geriatric (age 55+ years). Since 1990, Florida has used a uniform set of eight triage criteria, known as the trauma scorecard, for triaging adult trauma patients to state-approved trauma centers. However, only five of the criteria are recommended for use with pediatric patients. This article presents the findings regarding the performance of the scorecard when applied to a pediatric population.

DESIGN

We used state trauma registry data linked to state hospital discharge data in a retrospective analysis of trauma patients transported by prehospital providers to any acute care hospital within nine selected Florida counties between July 1, 1991, and December 31, 1991. We used cross-table and logistic regression analysis to determine the ability of triage criteria to correctly identify patients who were retrospectively defined as major trauma. We applied the field criteria to physiologic and anatomy/mechanism of injury data contained in the trauma registry to "score" the patient as major or minor trauma. To make our retrospective determination of major or minor trauma we used the protocols developed by an expert medical panel as described by E. J. MacKenzie et al. (1990).

MAIN OUTCOME MEASURES

We calculated sensitivity, specificity, and the corresponding over- and undertriage rates by comparing patient classifications (major or minor trauma) produced by the triage criteria and the retrospective algorithm. We used logistic regression to identify which triage criteria were statistically significant in predicting major trauma.

RESULTS

Pediatric cases accounted for 9.2% of the total study population, 6.0% of all hospitalized cases, and 6.8% of all trauma deaths. Of the 1505 pediatric cases available for analysis, the triage criteria classified 269 cases as expected major trauma and 1236 cases as expected minor trauma. The retrospective algorithm classified 78 cases as expected major trauma and 1427 cases as expected minor trauma. The resulting specificity is 84.8% (15.2% overtriage), and the sensitivity is 66.7% (33.3% undertriage). Logistic regression indicated that, of the eight state-adopted field triage criteria, only the Glasgow coma score, ejection from vehicle, and penetrating injuries have a statistically significant impact on predicting major trauma in pediatric patients.

CONCLUSIONS

Although the state-adopted trauma scorecard, applied to a pediatric population, produced acceptable overtriage, it did not produce acceptable undertriage. However, our undertriage rate is comparable to the results of other published studies on pediatric trauma. As a result of the Florida Trauma Triage Study, a new pediatric triage instrument was developed. It is currently being field-tested.

Conformational changes associated with activation of bee venom phospholipase A2

Bee venom PLA2 possesses a binding site for long-chain fatty acids that can be acylated by long-chain fatty acid imidazolides [Drainas, D. and Lawrence, A.J. (1978) Eur. J. Biochem. 91, 131-138]. Occupation of the site either by oleic acid or the oleoyl residue enhances the catalytic activity by 45.7-fold in the presence of 20% 1-propanol and occupation of the site by the oleoyl residue increases the lytic activity against rabbit erythrocytes by 60-fold. Treatment of the enzyme with oleic acid and glutaraldehyde is known to produce irreversible activation [Lawrence, A.J. and Moores, G.R. (1975) FEBS Lett. 49, 287-291]. Here we show that reduction of the glutaraldehyde-treated enzyme with borohydride stabilizes the activated state and enables the fatty acid to be removed, revealing that a large proportion of the induced activation does not require the presence of oleic acid and indicating that activation is due to a change in the conformation rather than the hydrophobicity of the protein. A kinetic study of enzyme activated by oleoyl imidazolide showed that this modification stabilizes the protein against reversible inactivation by 1-propanol. Comparison of the CD spectra of native and oleoyl imidazolide-activated enzyme shows a change in secondary structure with apparent increase in both alpha-helix and beta-sheet content. During reaction of the enzyme with oleoyl imidazolide, the protein fluorescence shows a biphasic response with an initial fall attributed to occupation of the binding site followed by a progressive decrease with a shift of the emission maximum from 341 to 348 nm. The rate of the second phase closely matched the rate of increase in catalytic activity of the enzyme. Free oleic acid caused a rapid fall in fluorescence emission without the subsequent slow change. These results support the proposal that oleic acid or the oleoyl residue occupy a very similar site on the protein and that occupation of this site increases the exposure of one or both of the Trp residues to the aqueous environment. Binding studies show that activation by oleoyl imidazolide does not increase the affinity of the enzyme for the erythrocyte membrane. It is proposed that occupation of a long-chain fatty acid binding site on the enzyme enhances catalytic activity by changing the conformation of the protein rather than acting as a hydrophobic anchor to the substrate surface.

Ligand-induced conformational changes in wild-type and mutant yeast pyruvate kinase

A mutant form of pyruvate kinase in which serine 384 has been mutated to proline has been engineered in the yeast Saccharomyces cerevisiae. Residue 384 is located in a helix in a subunit interface of the tetrameric enzyme, and the mutation was anticipated to alter the conformation of the helix and hence destabilize the interface. Previous results indicate that the mutant favours the T quaternary conformation over the R conformation, and this is confirmed by the results presented here. Addition of phosphoenol-pyruvate (PEP), ADP and fructose-1, 6-bisphosphate (Fru-1.6-P2) singly to the wild-type and mutant enzymes results in a significant quenching of tryptophan fluorescence (12-44%), and for Fru-1,6-P2, a red shift of 15 nm in the emission maximum. Fluorescence titration experiments showed that PEP, ADP and Fru-1,6-P2 induce conformations which have similar ligand-binding properties in the wild-type and mutant enzymes. However, the Fru-1,6-P2 induced conformation is demonstrably different from those induced by either ADP or PEP. The enzymes differ in their susceptibility to trypsin digestion and N-ethylmaleimide inhibition. The thermal stability of the enzyme is unaltered by the mutation. Far-UV CD spectra show that both enzymes adopt a similar overall secondary structure in solution. Taken together, the results suggest that the Ser384-Pro mutation causes the enzyme to adopt a different tertiary and/or quaternary structure from the wild-type enzyme and affects the type and extent of the conformational changes induced in the enzyme upon ligand binding. A simplified minimal reaction mechanism is proposed in which the R and T states differ in both affinity and kcat. Thus, in terms of the models of cooperativity and allosteric interaction, pyruvate kinase is both a K and a V system.