Amino acids biosynthesis and nitrogen assimilation pathways: a great genomic deletion during eukaryotes evolution.

BACKGROUND: Besides being building blocks for proteins, amino acids are also key metabolic intermediates in living cells. Surprisingly a variety of organisms are incapable of synthesizing some of them, thus named Essential Amino Acids (EAAs). How certain ancestral organisms successfully competed for survival after losing key genes involved in amino acids anabolism remains an open question. Comparative genomics searches on current protein databases including sequences from both complete and incomplete genomes among diverse taxonomic groups help us to understand amino acids auxotrophy distribution. RESULTS: Here, we applied a methodology based on clustering of homologous genes to seed sequences from autotrophic organisms Saccharomyces cerevisiae (yeast) and Arabidopsis thaliana (plant). Thus we depict evidences of presence/absence of EAA biosynthetic and nitrogen assimilation enzymes at phyla level. Results show broad loss of the phenotype of EAAs biosynthesis in several groups of eukaryotes, followed by multiple secondary gene losses. A subsequent inability for nitrogen assimilation is observed in derived metazoans. CONCLUSIONS: A Great Deletion model is proposed here as a broad phenomenon generating the phenotype of amino acids essentiality followed, in metazoans, by organic nitrogen dependency. This phenomenon is probably associated to a relaxed selective pressure conferred by heterotrophy and, taking advantage of available homologous clustering tools, a complete and updated picture of it is provided.

Managing venous thromboembolism in Latin American patients: emerging results from the Brazilian Registry.

A Brazilian National Registry was established in 1999 to investigate the incidence of risk factors for venous thromboembolism (VTE) in hospitalized medical and surgical patients and to investigate the use of thromboprophylaxis in these populations. A 4-year pilot study confirmed the feasibility and value of a registry project in this region, showing a dramatic increase in the use of low-molecular-weight heparin (LMWH) over the study period, associated with a sixfold reduction in the incidence of symptomatic VTE. Data on more than 27,000 patients from the Brazilian Registry have revealed that almost 25% of high-risk patients and 45% of those at moderate risk currently receive no thromboprophylaxis. Among the high-risk patients-in whom general measures alone are not considered appropriate prophylaxis-42% of patients did not receive pharmacological prophylaxis with either LMWH or unfractionated heparin. The Brazilian Registry highlights the need to raise awareness of VTE risk factors and recommended prophylactic regimens in Latin America.