Reaction mechanisms of flavins and flavoproteins from an electronic-structure perspective / Mecanismos de reação de flavinas e flavoproteínas por uma perspectiva de estrutura eletrônica

Proteins equipped with flavin adenine dinucleotides (FAD) or flavin mononucleotides (FMN) are named flavoproteins and constitute about 1% of all existing proteins. They catalyze redox, acid-base and photochemical reactions in a variety of biochemical phenomena that goes from energy metabolism to DNA repair and light sensing. The versatility observed in flavoproteins is ultimately a balance of flavin intrinsic properties modulated by a protein environment. This thesis aims to investigate how flavoproteins work by systematic evaluating flavin properties and reactivity. In particular, the mechanism of fumarate reduction by the flavoenzyme fumarate reductase Fcc3 was determined. Electronic-structure calculations were used for this task based on rigorous calibration with experimental data and error assessment. Flavin properties at chemical accuracy were obtained with single reference coupled-cluster CCSD(T) calculations at the complete basis set limit. Density functional theory was demonstrated an excellent alternative with lower computational costs and slightly less accuracy. Flavin protonation and tautomerism were shown to be important modulators of flavin properties and reactivity, with the possibility of various tautomers existing at neutral pH. Regarding flavin redox properties, an analysis based on multiconfigurational wave function weights was proposed for categorizing flavin redox reactions as hydride or hydrogen-atom transfers. This analysis is an upgrade over traditional partial charges methods and can be applied not only to flavin reactions but to any protoncoupled electron transfer. In the investigation of the enzymatic mechanism of fumarate reduction, the reaction was determined as a nucleophilic addition by hydride transfer with carbanion formation. Fumarate reductase employs electrostatic catalysis in contrast to previous proposals of substrate straining and general-acid catalysis. Also, hydride transfer was shown to be vibronically adiabatic with low tunneling contribution. These findings give new insights into the mechanisms of fumarate reductases and provide a framework for future computational studies of flavoproteins in general. The analyses and benchmark studies presented can be used to build better models of properties and reactivity of flavins and flavoproteins

Proteínas equipadas com dinucleotídeos de flavina-adenina (FAD) e mononucleotídeos de flavina (FMN) são chamadas flavoproteínas e constituem cerca de 1% de todas as proteínas existentes. Elas catalisam reações redox, ácido-base e fotoquímicas numa variedade de fenômenos bioquímicos que vão desde o metabolismo energético até reparo de DNA e captação de luz. A versatilidade observada em flavoproteínas é em última instância um balanço das propriedades intrínsecas de flavinas moduladas por um ambiente proteico. Esta tese busca investigar como flavoproteínas funcionam através de avaliações sistemáticas de propriedades e reatividade de flavinas. Em particular, o mecanismo de redução de fumarato pela flavoenzima fumarato redutase Fcc3 foi determinado. Cálculos de estrutura eletrônica foram usados para esta tarefa com base em rigorosa calibração com dados experimentais e avaliação de erros. As propriedades de flavinas foram determinadas com acurácia química com cálculos monoconfiguracionais de coupled-cluster CCSD(T) no limite de conjunto base completo. A teoria do funcional da densidade mostrou-se uma alternativa excelente com menor custo computacional e um pouco menos de acurácia. Protonação e tautomerismo de flavinas mostraram-se moduladores importantes de suas propriedades e reatividade, com a possibilidade de vários tautômeros existirem em pH neutro. Em relação às propriedades redox de flavinas, uma análise baseada nos pesos de funções de onda multiconfiguracionais foi proposta para categorizar as reações redox de flavinas como transferências de hidreto ou hidrogênio. Esta análise é uma melhoria em relação aos métodos tradicionais de cargas parciais e pode ser aplicada não apenas para reações de flavinas mas para qualquer transferência de próton acoplada a elétrons. Na investigação do mecanismo enzimático de redução de fumarato, a reação foi designada como uma adição nucleofílica por transferência de hidreto e formação de carbânion. A fumarato redutase usa catálise eletrostática diferentemente de prospostas anteriores envolvendo distorção do substrato e catálise ácida geral. Além disso, a transferência de hidreto mostrou-se vibronicamente adiabática com pouca contribuição de tunelamento. Estas descobertas abrem novas perspectivas sobre os mecanismos de fumarato redutases e fornecem uma base para estudos computacionais futuros sobre flavoproteínas em geral. As análises e estudos comparativos apresentados podem ser usados para construir melhores modelos para propriedades e reatividade de flavinas e flavoproteínas

Pancreatic calculi-Radiological features and diagnostic significance

Pancreatic calculi refers to true stones in the duct system of the pancreas. False stones are calcifications in the parenchyma of the gland. According to Mayo Robson pancreatic calculi never forms in a healthy pancreas. It is a diagnostic feature of chronic pancreatitis. and it is rare in acute pancreatitis except as its sequelae in areas of fat necrosis and in the wall of pseudocysts. Pancreatic calculi was first observed and recorded by Graaf in 1667. Later, Morgagni [1765] and Cawley [1788] reported autopsy findings of the stones. Capparelli [1883] is given credit for the first surgical removal of pancreatic calculi

Litiasis biliar en niños: un estudio clínico-morfológico / Clinical and morphological features of choletithiasis in children

Background: The use of ultrasonography increased the frequency of diagnosis of cholelithiasis in childhood. Aim: To determine the clinical and laboratory features and follow up of children with biliary stones. Patients and methods: Twenty six children (13 male, aged 1 month to 14 years) were prospectively enrolled. Results : Nine children had a past medical history of factors potentially predisposing to stones. A clinical presentation with vomiting (50 percent), abdominal pain (46 percent) and jaundice (23 percent) was the most common indication for surgery. The diagnosis was based on abdominal ultrasound in all children. Cholecystectomy was performed in 15 children (laparoscopy in 13 and open surgery in 2). Children who underwent surgery were older than those who did not undergo surgery (p <0.001), but they did not have differences in liver function tests. Eight children had pigmented stones and seven had cholesterol stones. Conclusions : In our patients, neither family history nor laboratory tests were useful in the diagnosis as well as in the clinical decision of surgery, which was based on symptoms. The presence of cholesterol stones in a high proportion of these children may be a unique situation in Chile, considering the high prevalence of this disease in the adult population

Urinary Stones following Renal Transplantation

BACKGROUND: The formation of urinary tract stones following renal transplantation is a rare complication. The clinical features of stones after transplantation differ from those of non-transplant patients. Renal colic or pain is usually absent and rarely resembles acute rejection. METHODS: We retrospectively studied 849 consecutive kidney transplant patients in The Rogosin Institute/The Weill-Cornell Medical Center, New York who were transplanted between 1980 and 1997 and had functioning grafts for more than 3 months, to determine the incidence of stone formation, composition, risk factors and patient outcome. RESULTS: At our center, urinary stones were diagnosed in 15 patients (1.8%) of 849 functioning renal grafts for 3 or more months. Of the 15 patients, 10 were males and 5 were females in their third and fourth decade. Eight patients received their transplant from living donors and 7 from cadaveric donors. The stones were first diagnosed between 3 and 109 months after transplantation (mean 17.8 months) and 5 patients had recurrent episodes. The stones were located in the bladder in 11 cases (73.3%), transplanted kidney in 3 cases and in multiple sites in one case. The size of stones varied from 3.4 mm to 40 mm (mean 12 mm). The composition of stones was a mixed form of calcium oxalate and calcium phosphate in 5 cases and 4 patients had infected stones consisting of struvite or mixed form of struvite and calcium phosphate. Factors predisposing to stone formation included tertiary hyperparathyroidism (n=8), hypercalciuria (n=5), recurrent urinary tract infection (n=5), hypocitraturia (n=4), and obstructive uropathy (n=2). Many cases had more than one risk factor. Clinically, painless hematuria was observed in 6 patients and dysuria without bacteriuria in 5 patients. None had renal colic or severe pain at any time. There were no changes in graft function at diagnosis and after removal of stones. Five patients passed stones spontaneously and 8 patients underwent cystoscopy for stone removal. CONCLUSION: Urinary stone formation following kidney transplantation is a rare complication (1.8%). Hyperparathyroidism, hypercalciuria, recurrent urinary tract infection and hypocitraturia are the most common risk factors, but often there are multiple factors which predispose to stone formation. To detect stones and determine their location and size, ultrasonography appears to be the most useful diagnostic tool. Prompt diagnosis, the removal of stones and stone-preventive measures can prevent adverse effects on renal graft outcome.

Cholesterol vs pigment cholelithiasis evaluation of sone clincal and citological risk factors

The present study was carried out at the Basic Medical Sciences Institute Jinnah Postgraduate Medical Centre, Karachi. To evaluate few of the risk factors associated with development of cholelithiasis in our population. Total of sixty patients having gallstones and 25 age and sex matched controls were included. The qualitative analysis of stones was done into chloesterol or the pigment type. Various factors like age and sex, obesity, parity, jaundice and familial tendency was observed and recorded. We concluded that female sex, multiparity, obesity, use of oral contraceptives and familial tendency are few of the risk associated with development of cholesterol gall stones while these factors do not seem to have any relation with pigment type of stones

Giant tonsillolith presenting as a neck swelling

A giant tonsillolith in a 30 year old man presented with swelling in left submandibular region. Stone weighing 15.5 grams was found in the left tonsil, composed mainly of calcium and magnesium phosphate and carbonate