Analysis of conformational states of Candida rugosa lipase in solution: implications for mechanism of interfacial activation and separation of open and closed forms

In this study, an analysis of the transition between the inactive ("closed") and active ("open") conformations of Candida rugosa lipase in solution is performed using irreversible enzyme inhibitors, cyclic saligenin phosphates. It is shown that >90% inhibition of the enzyme activity toward water-soluble substrates (esterolytic activity) can be achieved with as little as 0.3 mol of the inhibitor per mole of enzyme, whereas activity toward emulsified substrates decreases by approximately 20% under the same conditions. It is also shown that short-term exposure of this inhibited enzyme preparation to an interface leads to a significant increase in esterolytic activity, which even exceeds that of the untreated control. These experimental observations suggest that the inhibitors interact predominantly, if not exclusively, with the open form of the enzyme and that any transitions occurring between the two conformers of the enzyme in solution, in the absence of an interface, are extremely slow. This conclusion is verified by separating the open and closed forms of the enzyme by hydrophobic interaction column chromatography on phenyl-sepharose. Fractions enriched with the respective conformations of the enzyme are further purified using gel-permeation chromatography. On the basis of the elution pattern from this step, and sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the open (active in the absence of interface) form of the lipase is found to be present in solution as a dimer, whereas the closed form appears to be a monomer. The latter form of the enzyme may be activated by up to 60-fold when exposed to triolein.

Detection of tomato leaf curl geminivirus in its vector Bemisia tabaci

Geminiviruses are single-stranded DNA plant infecting viruses that cause major losses in important crops in tropical and subtropical countries. Tomato leaf curl virus (TLCV) belonging to the genera Begomovirus, is a whitefly-transmitted geminivirus that causes a severe leaf curl disease in tomato (Lycopersicon esculentum). The importance of this disease has prompted a great need for a rapid identification of TLCV in its hosts and vector. Polymerase chain reaction (PCR) is the most sensitive approach to detect a minute amount of viral nucleic acid. It is the most ideal method to amplify geminiviruses as they replicate via a double-stranded, circular DNA form. In this study, geminivirus specific degenerated primers were employed to detect TLCV occurring in its vector whitefly Bemisia tabaci by PCR based approach. One primer pair, amplified TLCV DNA fragment of about 1.1 Kb representing partly replicase gene, intergenic region and partly coat protein gene was used. When a set of primer targeted to the core region of the coat protein gene of geminivirus was used, a PCR amplified fragment of about 0.5 Kb was obtained. This approach is highly useful for an early detection of TLCV occurring in very small amount in the vector B. tabaci. Its implications in geminivirus management strategies and their differentiation and being discussed.

Production of sulfur flavors by ten strains of Geotrichum candidum

Ten strains of Geotrichum candidum were studied on a liquid cheese model medium for the production of sulfur compounds which contribute to the aroma of cheeses. The volatile components produced by each cultured strain were extracted by dynamic headspace extractions, separated and quantified by gas chromatography (GC), and identified by GC-mass spectrometry. It was shown that four strains of this microorganism produced significant quantities of S-methyl thioacetate, S-methyl thiopropionate, S-methyl thiobutanoate, S-methyl thioisobutanoate, S-methyl thioisovalerate, and S-methyl thiohexanoate. This is the first example of the production of these compounds by a fungus. In addition, dimethyldisulfide, dimethyltrisulfide, dimethylsulfide, and methanethiol, which are more commonly associated with the development of cheese flavor in bacterial cultures, were also produced by G. candidum in various yields, depending on the strain selected. The potential application of these strains in cultured microbial associations to produce modified cheeses with more desirable organoleptic properties is discussed.

Combinatorial approach to flavor analysis. 1. Preparation and characterization of a S-methyl thioester library

A new method for the "one-pot" synthesis of S-methyl thioesters has been developed by reacting methyl chlorothiolformate with carboxylic acids. The resulting "flavor library" contained all the intended thioesters and a single major impurity, identified by GC-MS as S, S-dimethyldithiocarbonate. Quantification of individual compounds present in the library was performed by GC analysis using two independent methods of detection, SCD and FID. It was shown that apart from S-methyl thioacetate (0.8 mol %), molar concentrations of other thioesters varied in a relatively narrow range from 4.2 mol % for S-methyl thiopropionate to 14.1 mol % for S-methyl thiohexanoate. In general, medium chain S-methyl thioesters were present in slightly higher molar concentrations than those prepared from short or long chain carboxylic acids. This variation was attributed to partial loss of the most volatile components during extraction and the lower reactivity of higher homologues. The library was used for the characterization of some physicochemical parameters of thioesters. In particular, lipophilicity coefficients (log k(w)) and thioester retention in 10, 20, and 33% triolein (used as a model lipid phase) were determined directly by reverse-phase HPLC and extrapolated from the respective data. This analysis illustrates that substantial information can be generated using a library containing a relatively large number of compounds in effectively the same way as is necessary for the analysis of a single sample.

Combinatorial approach to flavor analysis. 2. Olfactory investigation of a library of S-methyl thioesters and sensory evaluation of selected components

The odor characteristics of individual components present in a library comprised of S-methyl thioesters were determined independently by two laboratories using similar but not identical techniques. The odor potency was assessed by values of best estimate-GC-lower amount detected by sniffing (BE-GC-LOADS). For small and medium chain S-methyl thioesters, these values were found to increase from 6 ng for S-methyl thiobutanoate to 90 ng for S-methyl thiostearate. All assessors detected a "green", "floral", or "pineapple" odor for S-methyl thiohexanoate and described thioesters containing a 2-6 carbon chain length as "cheesy". The results of this preliminary analysis were confirmed by a more extensive study of selected compounds, namely S-methyl thioacetate, S-methyl thiopropionate, S-methyl thiobutanoate, and S-methyl thiohexanoate, using a trained panel of 18 subjects. The subjects confirmed the presence of the "green" and "fruity" notes in the odor of S-methyl thiohexanoate. The analysis also revealed a significant difference in the odor of S-methyl thiopropionate relative to that of S-methyl thioacetate and S-methyl thiobutanoate. When "cheesy" characteristics were mentioned, the majority of panelists clearly associated the flavor of S-methyl thiopropionate with Camembert with almost 20% of all the descriptors given referring specifically to this cheese variety as compared to about 2 and 5% in the case of S-methyl thioacetate and thiobutanoate, respectively. Prompted by this observation, two samples of Camembert prepared from unpasteurized and pasteurized milk were analyzed and relatively large amounts of S-methyl thiopropionate were found in the former but not in the latter cheese. The results obtained in the course of this work suggest that the sensory analysis of combinatorial libraries is a useful new approach in the search for new commercial flavors and/or identification of characteristic flavors in foods.

Epidemiology and clinical profile of HIV/AIDS in Pakistan

This study reviews available data on HIV/AIDS in Pakistan and is the first to analyse a clinical series of HIV-infected patients thus giving a wider perspective of the epidemic in Pakistan. A retrospective analysis of all medical records of patients with HIV/AIDS since 1986 was conducted in March 1998 at a Karachi hospital. There were 67 patients. Twenty-two were overseas (Middle East) contract workers. None were sex workers or drug users. Fifty-four had travelled or lived abroad. High risk sexual behaviour was reported in 35 patients of whom 26 men reported contact with commercial sex workers, mostly in the Middle East (21). The most common AIDS indicator condition was chronic diarrhoea. HIV in Pakistan is currently a disease of those Pakistanis (and their sexual partners) who have travelled abroad, overseas contract workers and those who, prior to 1989, were transfused abroad or received imported blood products.

Kinetic analysis of cyclic CMP-specific and multifunctional phosphodiesterases by quantitative positive-ion fast-atom bombardment mass spectrometry

Two enzymes, cyclic CMP-specific phosphodiesterase and multifunctional phosphodiesterase, are responsible for the hydrolysis of cytidine 3',5'-cyclic monophosphate in living cells. Quantitation of both enzymes has been carried out by positive-ion fast-atom bombardment mass spectrometric analysis of the enzyme incubates after termination of the reaction. The kinetic data obtained are in close agreement with parallel data obtained by the conventional radiometric assay. The extra facility of the mass spectrometry based assay to monitor several incubation components simultaneously has been exploited to study the concurrent hydrolysis of alternate cyclic nucleotide substrates and provides kinetic parameters of significance in interpreting substrate-enzyme interactions. This is extended by the use of collisionally-induced dissociation of the protonated molecules of the liberated products to identify the mononucleotide isomers resulting from the cyclic nucleotide hydrolysis.

A novel approach to biotransformations in aqueous-organic two-phase systems: enzymatic synthesis of alkyl beta-[D]-glucosides using microencapsulated beta-glucosidase

A novel approach to enzymatic biotransformations in aqueous-organic two-phase systems was developed where the aqueous phase was contained within permeable polymeric capsules suspended in organic solvent. Microencapsulated beta-glucosidase, used as a model enzyme, was shown to retain its catalytic activity for a considerable time and was repeatedly used in batch experiments after recharging the microcapsules with solid glucose. The reaction conditions for the synthesis of hexyl beta-[D]-glucopyranoside were optimized with regard to the polymer composition of the microcapsules, pH, and the volume ratio of aqueous to organic phases. The potential for further improvement in the efficiency of the system was demonstrated by designing a bioreactor which incorporated units for product recovery and recycling of the organic solvent. Other advantages of the proposed methodology include facile control over the size and composition of the microcapsules, and mild reaction conditions during their preparation.

Toxicity and therapeutic efficacy of amphotericin B delivered through cholesterol hemisuccinate vesicles in the treatment of experimental murine aspergillosis

We have studied the toxicity and therapeutic efficacy of amphotericin B in cholesterol hemisuccinate vesicles (ABCV) in the treatment of invasive aspergillosis in Balb/c mice. The toxicity of amphotericin B was significantly reduced when delivered through cholesterol hemisuccinate vesicles as compared to deoxycholate suspension (AmB(DOC)) as evidenced by reduced nephrotoxicity in Balb/c mice, lower in-vitro toxicity to erythrocytes and higher maximum tolerated dose. The latter increased from 2 mg/kg wt for AmB(DOC) to 17 mg/kg wt for ABCV. The vesicles had a mean diameter of 252 nm. In order to evaluate the therapeutic efficacy of ABCV, Aspergillus fumigatus-infected mice were treated with ABCV 2, 4, 8 or 12 mg/kg or AmB(DOC) 1 mg/kg wt. The antifungal activity was highly dependent on the dosage of ABCV on the basis of survival of treated mice and cfu in lung, liver, spleen and kidney. This study found that ABCV had dose-dependent antifungal activity and therapeutic efficacy in the treatment of invasive aspergillosis in Balb/c mice.

Role of fibreoptic bronchoscopy in the management of immunocompromised patients with pulmonary infiltrates

Immunocompromised patients are prone to develop various pulmonary complications. The range of diagnostic possibilities is wide, infection being the commonest cause. Non-invasive diagnostic tests are often unrewarding. In this study, we have evaluated the diagnostic efficacy and safety of fibreoptic bronchoscopy in immunocompromised patients with pulmonary infiltrates. Patients tolerated the procedure well. This technique identified the etiology in up tp 75% of cases. After treatment based on the result of bronchoscopy, 63% patients improved and were discharged.

Detection of plant viruses--biotechnological and molecular advances

Recent advances in biotechnology and molecular biology have played a significant role in development of rapid, specific and sensitive assays for detection of plant viruses. Production of monospecific polyclonal antibodies, monoclonal antibodies have enabled to group isolates of viruses and distinction of closely related strains. In cDNA hybridization applications, there is an increasing interest to employ non-radioactive probes for detection of nucleic acids. Detection limit of nucleic acid is remarkably comparable to those of radioactive labelled probes. Application of polymerase chain reaction (PCR) has made it possible to amplify the low numbers of viral RNA/DNA molecules and their subsequent detection. Underlying principles, their advantages and disadvantages for application of monospecific polyclonal antibodies, hybridoma technology, molecular hybridization and PCR technology with reference to detection of plant viruses have been discussed in this review.

Physician compliance with national tuberculosis treatment guidelines: a university hospital study

SETTING

The Aga Khan University Hospital, in Karachi, Pakistan, is a 650-bed university teaching hospital.

OBJECTIVES

There is little data from Pakistan on the awareness and application of the World Health Organization (WHO)'s tuberculosis treatment guidelines among physicians. This study evaluates physician compliance with these guidelines.

DESIGN

A questionnaire to measure physician compliance was developed, pilot tested and standardised. Case records of all patients hospitalized with tuberculosis were reviewed (January-December 1995, n = 229), and were classified into WHO Category 1 (n = 191), Category 2 (n = 9) and Category 3 (n = 29).

RESULTS

A total of 53 (23%) patients had a diagnostic bacteriological sputum smear examination, of which 38% were smear positive and 47% culture positive. Of 25 cerebrospinal fluid cultures 12% were positive. No sputum smear tests were conducted during treatment. Of 58 patients in Category 1 who completed therapy 74% received a 2-month intensive phase consisting of HRZE (isoniazid, rifampicin, pyrazinamide, ethambutol) (n = 43), while 41% received a 6 month continuation phase with HE (n = 24). Over 70% patients were lost to follow up, more than half of these during the intensive phase.

CONCLUSION

Our study reflects poor awareness of the WHO guidelines and low compliance among physicians, and a high loss to follow-up. Efforts are needed to create physician awareness about the WHO guidelines and their use. This study can be used to assess the effectiveness of any future physician education and to identify areas of weakness in health care.

RAND study: workforce requirements and provider supply relevant to oculoplastic and orbital surgery

The 1995 RAND study Estimating Eye Care and Workforce Requirements analyzes the United States' supply, demand, and need for eyecare providers. Portions of the RAND study were prepared along traditional ophthalmic specialty lines. This article extracts and further analyzes those portions of the study that are of interest to active subspecialty oculoplastic surgeons. The RAND study results indicate a significant current and very probable future oversupply of oculoplastics workforce personnel. This oversupply is further exacerbated when a RAND study underestimate of the number of new fellowship-trained oculoplastic surgeons is corrected.

An epidemic of Dengue fever in Karachi--associated clinical manifestations

Dengue is a mosquito borne disease with worldwide distribution. Depending on virulence factors and host immune status, infection can manifest as a severe but non fatal viral syndrome or a rapidly progressive and a frequently fatal haemorrhagic fever. During the course of an outbreak of viral fever in Karachi, Pakistan from June, 1994 to September, 1995, we studied 145 cases admitted at the Aga Khan University Hospital. 43% of the cases were between the age group of 20-30 years, majority of these being male (75%). Amongst the clinical signs and symptoms, the most frequent findings were fever, vomiting and abdominal pain. Spontaneous hemorrhagic manifestations occurred in 66 patients and of these petechiae and mucosal bleed were the commonest, that is, 42% and 38% respectively. At presentation thrombocytopenia (platelet count < or = 50,000) per cubic millimeter) was present in 78%, leucopenia (white cell count < 4,000 per cubic millimeter) in 34%. Apart from one patient who died from hemorrhagic shock on the 5th day of admission, the remaining patients recovered and their platelet counts normalized on an average in 9 days. This is the first reported epidemic in Karachi of dengue infection.

Intracellular recordings from spinal neurons during ‘swimming’ in paralysed amphibian embryos

Intracellular microelectrode recordings have been made from probable moto- neurons in the spinal cord ofXenopus laevisembryos during Active ‘swimming’ in preparations paralysed with the neuromuscular blocking agent tubocurarine. These cells had resting potentials of -50 mV or more. During spontaneous or stimulus- evoked ‘swimming’ episodes: (a) the cells were tonically excited; the level of tonic synaptic excitation and the conductance increase underlying it were both inversely related to the ‘swimming’ cycle period; (b) the cells usually fired one spike per cycle in phase with the motor root burst on the same side; spikes did not overshoot zero and were evoked by phasic excitatory synaptic input on each cycle, superimposed on the tonic excitation; (c) in phase with motor root discharge on the opposite side of the body, the cells were hyperpolarized by a chloride-dependent inhibitory postsynaptic potential. The nature of synaptic potentials during ‘swimming’ was evaluated by means of intracellular current injections. The ‘swimming’ activity could be controlled by natural stimuli. The results provide clear evidence on the relation of tonic excitation to rhythmic locomotory pattern generation, and indirect evidence for reciprocal inhibitory coupling between antagonistic motor systems.

Analysis of metabolic pathways by the growth of cells in the presence of organic solvents

A new approach to the analysis of metabolic pathways involving poorly water-soluble intermediates is proposed. It relies upon the ability of the hydrophobic intermediates formed by a sequence of intracellular reactions to cross the membrane(s) and partition between aqueous and organic phases, when cells are incubated in the presence of a nonpolar and nontoxic organic solvent. As a result of this thermodynamically driven efflux of the formed intermediates from the cell, they accumulate in the organic medium in sufficient quantities for GC-MS analysis and identification. This enables direct determination of the sequence of chemical reactions involved with no requirement for the isolation of each individual metabolite from a cell-free extract. The feasibility of the proposed methodology has been demonstrated by the elucidation of the biosynthesis of (R)-gamma-decalactone from (R)-ricinoleic acid catalyzed by the yeast Sporidiobolus ruinenii grown in the presence of decane. The corresponding 4-hydroxy-acid intermediates, formed in the course of beta-oxidation of (R)-ricinoleic acid, were simultaneously observed in a single experiment on the same chromatogram. Potential applications of this proposed methodology are briefly discussed.