Enzyme activation through the utilization of intrinsic dianion binding energy

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We consider 'the proposition that the intrinsic binding energy that results from the noncovalent interaction of a specific substrate with the active site of the enzyme is considerably larger than is generally believed. An important part of this binding energy may be utilized to provide the driving force for catalysis, so that the observed binding energy represents only what is left over after this utilization' [Jencks,W.P. (1975) Adv. Enzymol. Relat. Areas. Mol. Biol. , , 219-410]. The large ~12 kcal/mol intrinsic substrate phosphodianion binding energy for reactions catalyzed by triosephosphate isomerase (TIM), orotidine 5'-monophosphate decarboxylase and glycerol-3-phosphate dehydrogenase is divided into 4-6 kcal/mol binding energy that is expressed on the formation of the Michaelis complex in anchoring substrates to the respective enzyme, and 6-8 kcal/mol binding energy that is specifically expressed at the transition state in activating the respective enzymes for catalysis. A structure-based mechanism is described where the dianion binding energy drives a conformational change that activates these enzymes for catalysis. Phosphite dianion plays the active role of holding TIM in a high-energy closed active form, but acts as passive spectator in showing no effect on transition-state structure. The result of studies on mutant enzymes is presented, which support the proposal that the dianion-driven enzyme conformational change plays a role in enhancing the basicity of side chain of E167, the catalytic base, by clamping the base between a pair of hydrophobic side chains. The insight these results provide into the architecture of enzyme active sites and the development of strategies for the de novo design of protein catalysts is discussed.

Bacillary disease and health seeking behavior among Filipinos with symptoms of tuberculosis: implications for control

SETTING

Urban and rural communities and urban poor settlements in the Philippines.

OBJECTIVE

To determine bacillary disease and action taking among individuals with symptoms of tuberculosis (TB), and to analyze their implications for TB control.

STUDY DESIGN AND METHOD

Subjects aged 20 years and older were interviewed in the 1997 nationwide stratified multi-cluster survey. Sputum acid-fast smears and cultures were done in subjects with abnormal screening chest radiographs.

RESULTS

Individuals with TB symptoms comprised 18.1% of the population studied. The prevalence of bacillary disease was 39/1000 in symptomatic subjects compared to 13/1000 in asymptomatic subjects. Symptom screening had a 14.3% positive predictive value and a 91.4% negative predictive value for bacillary disease. Significantly more symptomatic than asymptomatic subjects attended chest radiographic screening during the survey. However, in response to their symptoms, the majority (43.0%) took no action or self medicated (31.6%), while 11.8% consulted a private practitioner, 7.5% a public health center, 4.4% a hospital, and 1.7% a traditional healer.

CONCLUSION

Sputum smear examination after symptom screening was acceptable for case finding. The health seeking behavior of subjects with TB symptoms was inappropriate. A health education program and public-private collaboration in directly observed therapy, short course (DOTS) are essential for TB control in the Philippines.

BCG coverage and the annual risk of tuberculosis infection over a 14-year period in the Philippines assessed from the Nationwide Prevalence Surveys

SETTING

A prevalence survey of tuberculosis (TB) infection was undertaken in the Philippines, a developing country in the Western Pacific region.

OBJECTIVE

To determine the bacille Calmette Guerin (BCG) vaccination rate, the prevalence of TB infection and the annual risk of TB infection (ARTI).

METHODS

A nationwide stratified multi-stage cluster survey of 21,960 individuals. BCG scar verification and tuberculin test were performed on those aged > or =2 months. The ARTI was calculated using the prevalence rates of TB infection in children aged 5-9 years.

RESULTS

BCG scars were noted in 66% of the study population. The prevalence of TB infection was 63.4% among unvaccinated individuals. The prevalence rate was higher in males in both urban and rural areas. With both sexes combined, urban and rural communities had similar prevalence rates. In children aged 5-9 years, the prevalence rate was 16.1% (males 17.4%, females 14.9%), corresponding to an ARTI of 2.3% (males 2.5%, females 2.1%).

CONCLUSION

BCG coverage increased substantially between 1981-1983 and 1997. The ARTI, however, was virtually unchanged, indicating that morbidity due to TB continued to be high.

Tuberculosis in the urban poor settlements in the Philippines

SETTING

Urban poor settlements in the Philippines.

OBJECTIVE

To determine the magnitude of the tuberculosis problem in urban poor settlements in comparison with urban areas studied in the Nationwide Tuberculosis Prevalence Survey.

STUDY DESIGN AND METHOD

A multistage cluster survey of BCG scar, tuberculin test, chest radiography and sputum examination for bacillary disease, in urban poor areas.

RESULTS

The prevalences of culture-positive and smear-positive tuberculosis were 17.5 +/- 2.3 (95% CI 13.3-22.4) and 7.9 +/- 2.3 per thousand (95% CI 2.611.5), respectively. Extrapolated to the total population, the rates in the urban poor settlements were 12.4 +/- 1.7 (95% CI 9.6-16.2) and 5.6 +/- 1.6 per thousand population (95% CI 1.3-8.3), respectively. The prevalence of active pulmonary tuberculosis in subjects aged 10 years or more was 66 +/- 5.6/1000 (95% CI 55-77). The BCG vaccination rate was 72%. The overall prevalence of tuberculosis infection was 66%, and 39% in those aged 5-9 years, corresponding to an annual risk of infection (ARI) of 6.5%.

CONCLUSION

The problem of tuberculosis was substantial in the urban poor settlements, and was appreciably worse than that in the general urban population.

The 1997 Nationwide Tuberculosis Prevalence Survey in the Philippines

SETTING

The Philippines is a developing country where tuberculosis (TB) remains a significant public health problem.

OBJECTIVE

To determine the prevalence of TB as a basis for setting the targets of the National Tuberculosis Control Program.

STUDY POPULATION AND METHODS

A multi-stage cluster survey of a random sample of 21960 subjects from 36 clusters nationwide was undertaken from 2 April to 31 July 1997. BCG scar verification and tuberculin testing was performed for subjects aged 2 months and over, and chest radiography screening was done on subjects 10 years and older. Sputum samples were collected from individuals who were initially assessed to have abnormal chest radiographs to determine the prevalence of bacillary tuberculosis. Acid-fast smear by modified Kinyoun's technique and culture on Löwenstein Jensen were done to demonstrate Mycobacterium tuberculosis.

RESULTS

The prevalence of active pulmonary TB was 42/1000 population. The prevalence of culture-positive and smear-positive cases was 8.1 and 3.1/1000, respectively. The prevalence was similar in urban and rural areas.

CONCLUSION

Morbidity from TB remains high. Allowing for methodological differences from the survey in 1981-1983, the prevalence of active pulmonary TB was unchanged. There was only a minimal decrease, of 37% for smear-positive cases and 25% for culture-positive cases, in the 14-year interval.