Evidence that cysteine 298 is in the active site of tryptophan indole-lyase

Escherichia coli tryptophan indole-lyase (tryptophanase) mutants, with cysteine residues 294 and 298 selectively replaced by serines, have been prepared by site-directed mutagenesis. Both mutant enzymes are highly active for beta-elimination reactions measured with both L-tryptophan and S-(o-nitrophenyl)-L-cysteine. The Cys-294----Ser mutant enzyme is virtually identical to the wild type with respect to pyridoxal phosphate binding (KCO = 2 microM), cofactor absorption spectrum (lambda max = 420 and 337 nm) and pH dependence (pK alpha = 7.3), pH profile for catalysis, and rate of bromopyruvic acid inactivation. In contrast, the Cys-298----Ser mutant enzyme exhibits a reduced affinity for pyridoxal phosphate (KCO = 6 microM), a shift in the cofactor absorption spectrum to 414 nm and an altered pK alpha = 8.5, an alkaline shift in the pH profile for catalysis, and resistance to inactivation of the apoenzyme by bromopyruvic acid. The C298S mutant enzyme (wherein cysteine 298 is altered to serine) also undergoes an isomerization to an unreactive state upon storage at 4 degrees C. These results demonstrate that the sulfhydryl groups of Cys-294 and Cys-298 are catalytically nonessential. However, these data suggest that Cys-298 is located within or very near the active site of the enzyme and is the reactive cysteine residue previously observed by others.

Chlamydia trachomatis cervical infection in women seeking routine gynecologic care: criteria for selective testing

PURPOSE

Chlamydia trachomatis infection is one of the most common sexually transmitted diseases. Developing methods to identify patients who are at higher risk would enable clinicians to perform selective testing for C. trachomatis infection, which may reduce morbidity, sequelae, and overall costs. Risk factors for C. trachomatis infection of the cervix in women seen for routine gynecologic care were therefore analyzed.

PATIENTS AND METHODS

Extensive clinical data and cervical cultures were obtained from 1,141 women between the ages of 18 and 50. Multivariate techniques were used to develop and prospectively test a model to predict infection.

RESULTS

In the model development series of 530 patients seen in a hospital-based practice, 24 (4.5%) had a positive culture result. In the validation series of 611 patients seen in private practice, 17 (2.8%) had positive culture results. The majority of infected patients (61%) were asymptomatic. For sexually active women 18 to 35 years of age, the optimal predictive model was based on three factors: level of education (high school or less), a sex partner with other partners during the prior three months, and endocervical bleeding induced by the initial swab. In the validation series, the prevalence of infection for women with one or more of these factors was 5.8% (95% confidence interval, 4.0 to 8.6) compared with 0.9% in patients without these factors (p = 0.005).

CONCLUSION

Clinical information can be used in a low-prevalence population to predict a patient's risk for C. trachomatis infection and to select patients for testing.

Should women be tested for gonococcal infection of the cervix during routine gynecologic visits? An economic appraisal

PURPOSE, PATIENTS, AND METHODS

We used decision analysis to calculate the economic implications of routine testing for Neisseria gonorrhoeae infection of the cervix. This study compared performing endocervical cultures in all women seeking routine gynecologic care to a no-test strategy. Estimates derived from the medical literature were varied in a sensitivity analysis, and a Monte Carlo technique was used to incorporate the estimates of experts into the analysis.

RESULTS

We found that routinely testing for gonorrhea reduced overall medical costs when the prevalence of infection exceeded 1.5 percent. This result was most sensitive to variation in the cost of the culture and the assumption that treatment prevents adverse sequelae. Reducing the estimated cost of the culture from $9 to $5 decreased the threshold prevalence from 1.5 to 0.8 percent. When we considered the variation in estimates of experts, the threshold prevalence increased from 1.5 to 2.1 percent.

CONCLUSION

We conclude that a strategy of testing and treating selected women with risk factors for gonorrhea will not only reduce the likelihood of the development of serious adverse sequelae but will also result in a reduction of medical costs.

Interventions to prevent readmission. The constraints of cost and efficacy

Decision analysis was used to examine the interrelationship of cost and success for an intervention program designed to prevent unexpected readmissions to an acute care hospital. Three separate strategies were considered: 1) intervention for patients who are at high risk for unexpected readmission; 2) intervention for all patients who are admitted to the medical service; and 3) no intervention. Risk and cost data were derived from an analysis of 4,769 patients discharged from Boston's Beth Israel Hospital medical service during a 1-year period. It was found that interventions that cost $250.00 per patient could be cost saving given reasonable expectations of success. If an intervention for high risk patients costs $250.00 per patient, overall costs would be reduced if the success rate of the intervention was 9% or greater. If the success rate exceeded 17%, offering the intervention to all patients would reduce costs. If the cost of an intervention increases by a factor of two, it must be twice as likely to succeed to achieve the same economic benefit. Decision analysis provides a useful framework for evaluation of the economic implications of intervention strategies, and it is recommended that these methods be used in the planning and implementing of medical interventions.

The use of murine feeder cells in the cultivation of Plasmodium falciparum asexual blood stages

Increased multiplication rates were observed in asexual erythrocytic stages of Plasmodium falciparum grown in the presence of a feeder-cell layer of mouse peritoneal wash cells (PWCs) using the candle-jar method of Trager and Jensen (1977). This held true for both new and established isolates of the parasite. When the PWC population was separated into adherent and non-adherent fractions, the adherent PWC population promoted an increase in parasite growth but the non-adherent population did not. An increase in parasite multiplication was not promoted by PWC-conditioned medium.

Identification of factors associated with the diagnosis of delirium in elderly hospitalized patients

We analyzed factors associated with the discharge diagnosis of delirium among 1,285 patients admitted to a major teaching hospital during a 2-year period, developed a model to classify the risk of developing delirium on the basis of clinical and diagnostic data, and tested the model on 471 patients admitted during the subsequent year. Using the multivariate technique of recursive partitioning, we identified four factors that distinguished 80% of all cases of delirium: 1) a urinary tract infection at any time during the hospital stay (odds ratio = 3.1; 95% confidence interval = 2.02-4.58); 2) no urinary tract infection, but low serum albumin on admission (odds ratio = 2.4; 95% confidence interval = 1.43-3.99); 3) neither urinary tract infection nor low serum albumin, but elevated white blood cell count on admission (odds ratio = 1.99; 95% confidence interval = 1.18-3.37); 4) none of these risk factors, but proteinuria on admission (odds ratio = 1.82; 95% confidence interval = 1.25-2.66). Patients without any of these four risk factors had the lowest probability of developing delirium during their hospital stay. Among individuals with delirium, in-hospital mortality and hospital charges were higher. The model developed accurately characterized the risk of delirium when it was tested on patients admitted to the same hospital during the subsequent year.

The effects of morbid obesity and the Garren-Edwards gastric bubble on solid phase gastric emptying

Rapid solid phase gastric emptying (SPGE) resulting in decreased satiety is postulated to be a contributing factor to obesity. Twenty-six morbidly obese patients with a weight range of 189-523 lb were entered into the Garren-Edwards gastric bubble program. SPGE studies were performed pre-bubble implantation and repeated within 2 wk after bubble implant. There was no significant difference between study patients pre-bubble insertion emptying time and the normal population curve. Emptying time was found to be significantly increased, post-bubble implant, compared with pre-bubble implant over five time periods of testing. The Garren-Edwards gastric bubble has been used as a method for inducing early satiety for the morbidly obese patient. It has been postulated that delay of SPGE would be associated with satiety. Our patients experienced satiety despite their more rapid SPGE. Thus, the satiety which was experienced by our subjects was not on the basis of delayed SPGE, as previously thought.

Detection and identification of transient intermediates in the reactions of tryptophan synthase with oxindolyl-L-alanine and 2,3-dihydro-L-tryptophan. Evidence for a tetrahedral (gem-diamine) intermediate

The reactions of 2,3-dihydro-L-tryptophan (DHT) and oxindolyl-L-alanine (OXA) with tryptophan synthase have been investigated by rapid-scanning stopped-flow (RSSF) spectroscopy and by the concentration dependence of rates measured by single-wavelength stopped-flow (SWSF) spectroscopy. The RSSF spectral changes for DHT and OXA show the disappearance of the internal aldimine (lambda max 412 nm), the formation and decay of intermediates absorbing less than or equal to 340 nm, and the appearance of the quinonoid (lambda max 492 and 480 nm, respectively). Rate constants determined by SWSF were either well resolved (i.e., k1[DHT], k-1 greater than k2, k-2 greater than k3, k-3) or indicative of a tightly coupled system (i.e., k1[OXA], k-1 greater than or equal to k2, k-2 greater than k3, k-3). The RSSF spectral changes and SWSF kinetic studies together with computer simulations of the kinetic time courses are consistent with a mechanism that includes formation of a bleached species. Detection of these shorter wavelength species in the reactions of OXA and DHT indicates that substrate analogues with tetrahedral geometry at C-3 induce new protein-substrate interactions that result in the accumulation of species not previously detected in the tryptophan synthase system. The bleached species with lambda max less than or equal to 340 nm are proposed as the gem-diamine intermediates.

Mechanistic deductions from kinetic isotope effects and pH studies of pyridoxal phosphate dependent carbon-carbon lyases: Erwinia herbicola and Citrobacter freundii tyrosine phenol-lyase

The pH dependence of the kinetic parameters and primary deuterium isotope effects have been determined for tyrosine phenol-lyase from both Erwinia herbicola and Citrobacter freundii. The primary deuterium isotope effects indicate that proton abstraction from the 2-position of the substrate is partially rate-limiting for both enzymes. The C. freundii enzyme primary deuterium isotope effects [DV = 3.5 and D(V/Ktyr) = 2.5] are pH independent, indicating that tyrosine is not sticky (i.e., does not dissociate slower than it reacts to give products). Since Vmax for both tyrosine and the alternate substrate S-methyl-L-cysteine is also pH independent, substrate binds only to the correctly protonated form of the enzyme. For the E. herbicola enzyme, both Vmax and V/K for tyrosine or S-methyl-L-cysteine are pH dependent, as well as both DV and D(V/Ktyr). Thus, while both the protonated and unprotonated enzyme can bind substrate, and may be interconverted directly, only the unprotonated Michaelis complex is catalytically competent. At pH 9.5, DV = 2.5 and D(V/Ktyr) = 1.5. However, at pH 6.4 the isotope effect on both parameters is equal to 4.1. From these data, the forward commitment factor (cf = 5.2) and catalytic ratio (cvf = 1.1) for tyrosine and S-methyl-L-cysteine (cf = 2.2, cvf = 24) are calculated. Also, the Michaelis complex partition ratio (cf/cvf) for substrate and products is calculated to be 4.7 for tyrosine and 0.1 for S-methyl-L-cysteine.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanistic deductions from multiple kinetic and solvent deuterium isotope effects and pH studies of pyridoxal phosphate dependent carbon-carbon lyases: Escherichia coli tryptophan indole-lyase

Analysis of the pH dependence of the kinetic parameters and competitive inhibitor Ki values for tryptophan indole-lyase suggests two enzymic groups must be unprotonated in order to facilitate binding and catalysis of tryptophan. The V/K for tryptophan and the pKi for oxindolyl-L-alanine, a putative transition state analogue and competitive inhibitor, decrease below two pK values of 7.6 and 6.0, while the Ki for L-alanine, also a competitive inhibitor, is 3300-fold larger (20 mM) than that for oxindolyl-L-alanine and increases below a single pK of 7.6. A single pK of 7.6 is also observed in the V/K profile for the alternate substrate, S-methyl-L-cysteine. Therefore, the enzymic group with a pK of 7.6 is responsible for proton abstraction at the 2-position of tryptophan, while the enzymic group with a pK of 6.0 interacts with the indole portion of tryptophan and probably catalyzes formation of the indolenine tautomer of tryptophan (in concert with proton transfer to C-3 of indole from the group with pK 7.6) to facilitate carbon-carbon bond cleavage and elimination of indole. The pH variation of the primary deuterium isotope effects for proton abstraction at the 2-position of tryptophan (DV = 2.5 and D(V/Ktrp) = 2.8) are pH independent, while the Vmax for tryptophan or S-methyl-L-cysteine is the same and also pH independent. Thus, substrates bind only to the correctly protonated form of the enzyme. Further, tryptophan is not sticky, and the pK values observed in both V/K profiles are the correct ones.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of gastric bubble implant on weight change with and without compliance with a behavior modification program

The purpose of this prospective study was to evaluate the effect of compliance versus noncompliance with a behavior modification program (BMP) for 35 patients who underwent implantation of 51 Garren-Edwards gastric bubbles (GEGB). Criteria for morbid obesity was met by every patient. Two patient groups were formed by self-selection. Compliant patients (group I) attended 75% or more of the BMP. Group II consisted of noncompliant patients, and was divided further into partially complaint and totally noncompliant. A significant difference was found in both loss of weight and loss of body mass index (BMI) between the complaint and noncompliant groups, with no significant difference in weight loss between the partially and totally noncompliant groups. Patients' compliant or noncompliant behavior had a significant effect on changes in weight (p = 0.007) and body mass index (p = 0.005). Sixteen patients had two consecutive bubble implants. The rate of compliance was significantly higher during the first implant program, with a significantly greater loss in both weight and BMI for compliant patients. Follow-up data for 28 of 35 patients revealed a continued, albeit small, average weight decrease. In summary, weight loss does not result from the gastric bubble alone. Our study demonstrates that the key factor is compliance with a behavior modification program.

Gonorrhea in women seen for routine gynecologic care: criteria for testing

PURPOSE

This study was initiated to determine risk factors for Neisseria gonorrhoeae infection of the cervix in women seen for routine care in a hospital-based obstetrics and gynecology practice.

PATIENTS AND METHODS

Extensive clinical data and cervical culture specimens for N. gonorrhoeae were obtained prospectively from 1,441 women between the ages of 18 and 50. Fifty clinical factors were evaluated by multivariate analysis.

RESULTS

Of the 1,441 patients tested, 25 (1.7 percent) had a positive culture result. The majority of infected women were asymptomatic. The following five factors were found to be associated independently with gonococcal infection: (1) sex with a partner who may have had gonorrhea or a urethral discharge within the prior three months, (2) endocervical bleeding induced by the initial swab, (3) age at first intercourse less than or equal to 16, (4) method of payment (Medicaid), and (5) low abdominal or pelvic pain. Race, a univariate risk factor, was not associated with gonorrhea when these other factors were considered. The risk of infection for women with none, one, two, or three or more of these multivariate risk factors was 0.2, 0.8, 2.9, and 9.8 percent, respectively.

CONCLUSION

Clinical data are helpful in identifying women at risk for gonorrhea. If resources are insufficient to evaluate all sexually active women, we suggest routine testing based on the presence of the multivariate risk factors identified.

6-Nitro-L-tryptophan: a novel spectroscopic probe of trp aporepressor and human serum albumin

The binding of 6-nitro-L-tryptophan to trp aporepressor and human serum albumin has been examined by visible difference spectroscopy and circular dichroism. 6-Nitro-L-tryptophan, prepared by nitration of L-tryptophan with nitric acid in glacial acetic acid, exhibits a visible and near-uv absorption spectrum with lambda max at about 330 nm (epsilon = 7 X 10(3) M-1 cm-1) and a shoulder near 380 nm in H2O. In the presence of trp aporepressor, the visible absorption intensity is sharply diminished. Visible difference spectral titration data give KD = 1.27 X 10(-4) M and n = 0.95 per subunit at 25 degrees C. While 6-nitro-L-tryptophan exhibits no significant circular dichroism between 300 and 500 nm, the complex with trp aporepressor exhibits strong circular dichroism signals, with a negative maximum at 386 nm (delta epsilon = -7.5 M-1 cm-1) and a positive maximum at 310 nm (delta epsilon = +6 M-1 cm-1). Circular dichroism titration data give KD = 1.69 X 10(-4) M and n = 0.90 per subunit at 25 degrees C. The KD values determined spectroscopically are in excellent agreement with that determined by equilibrium dialysis, KD = 1.5 X 10(-4) M at 25 degrees C. In the presence of human serum albumin, the spectrum of 6-nitro-L-tryptophan exhibits a blue shift and an increase in absorption intensity; similar changes are observed in solvents of low dielectric contrast such as 80% aqueous dioxane. Visible difference spectral titration data give KD = 8.0 X 10(-5) M and n = 0.95 for human serum albumin. The complex of 6-nitro-L-tryptophan with human serum albumin exhibits a strong positive circular dichroism maximum at 380 nm (delta epsilon = +9.8 M-1 cm-1) with a shoulder at 310-320 nm. Circular dichroism titration data give KD = 6.4 X 10(-5) M and n = 0.83, in good agreement with the visible difference spectral results. Taken together, our results demonstrate the utility of 6-nitro-L-tryptophan as a spectroscopic probe for tryptophan-binding proteins.

Age as a risk factor in colonoscopy: fact versus fiction

Age has been assumed to be an independent risk factor in patients undergoing colonoscopy. However, this has never been specifically studied. We evaluated 302 patients 65 yr old or older, to determine the incidence of complications. We found that the risk is comparable to that of the heterogeneous patient population previously reported, except for a slightly increased incidence of delayed bleeding subsequent to polypectomy. In addition, the presence of cardiac, pulmonary, liver, or kidney disease was not found to be associated with an increased incidence of complications. Neither was there an increased risk of complications in patients undergoing colonoscopy, who had previously undergone abdominal or pelvic surgery. In summary, older patients experience the same risks as younger patients, except for post-polypectomy delayed bleeding, which may be related to atherosclerosis of the blood vessels, and appears to be more common in elderly patients.

Predicting emergency readmissions for patients discharged from the medical service of a teaching hospital

Emergency readmissions among patients discharged from the medical service of an acute-care teaching hospital were analyzed. Using the multivariate technique of recursive partitioning, the authors developed and validated a model to predict readmission based on diagnoses and other clinical factors. Of the 4,769 patients in the validation series, 19% were readmitted within 90 days. Twenty-six per cent of the readmissions occurred within ten days of discharge, and 57% within 30 days. Readmitted patients were older, had longer hospitalizations, and had greater hospital charges (p less than 0.01). The discharge diagnoses of AIDS, renal disease, and cancer were associated with increased risks of readmission regardless of patients' demographics or test results. The relative risks (95% confidence interval) associated with these diagnoses were: AIDS, 3.3 (1.4-7.8); renal disease, 2.3 (1.7-3.0); cancer, 2.8 (2.4-3.4). Other patients at increased risk were those with diabetes, anemia, and elevated creatinine (2.1; 1.6-2.8) and those with heart failure and elevated anion gaps (2.2; 1.7-2.8). For patients without one of these diagnoses, a normal albumin and no prior admission within 60 days identified patients at reduced risk for readmission (0.4; 0.3-0.4). Thus, commonly available clinical data identify patients at increased risk for emergency readmission. Risk factor profiles should alert physicians to these patients, as intensive intervention may be appropriate. Future studies should test the impacts of clinical interventions designed to reduce emergency readmissions.

Use of a direct fluorescent antibody test for detecting Chlamydia trachomatis cervical infection in women seeking routine gynecologic care

We determined the sensitivity, specificity, and predictive value of a direct fluorescence test for Chlamydia trachomatis infection compared with culture of the endocervix in women seeking routine gynecologic care. Of 527 patients seen in a hospital-based practice, 23 (4.4%) had a positive culture for C. trachomatis. The overall sensitivity of the direct test was 70%, and the specificity was 98%. When five or more endocervical cells were present on the direct test slide, the sensitivity increased to 92%, and the specificity decreased to 96% (P less than .05). When the presence of any columnar epithelial cells, five or more elementary bodies, or both was used as the criteria for accepting specimens, the sensitivity and specificity of the direct test were 80% and 96%, respectively. However, 44% of the specimens would be rejected if these criteria were used. The overall probability that an individual with a positive direct test would have a positive culture was 62%.