Hexokinase is the first enzyme in the glycolytic pathway, catalyzing the transfer of a phosphoryl group from ATP to glucose to form glucose 6-phosphate and ADP. Two yeast hexokinase isozymes are known, namely PI and PII. The crystal structure of yeast hexokinase PII from Saccharomyces cerevisiae without substrate or competitive inhibitor is determined and refined in a tetragonal crystal form at 2.2-Å resolution. The folding of the peptide chain is very similar to that of Schistosoma mansoni and previous yeast hexokinase models despite only 30% sequence identity between them. Distinct differences in conformation are found that account for the absence of glucose in the binding site. Comparison of the current model with S. mansoni and yeast hexokinase PI structures both complexed with glucose shows in atomic detail the rigid body domain closure and specific loop movements as glucose binds. A hydrophobic channel formed by strictly conserved hydrophobic residues in the small domain of the hexokinase is identified. The channel's mouth is close to the active site and passes through the small domain to its surface. The possible role of the observed channel in proton transfer is discussed.

This work deals with esterification of palm fatty acids to produce biodiesel in a batch reactor, using homogeneous acid catalysts, evaluating the effect of the alcohol used, presence of water, type and concentration of catalysts. Methanesulfonic and sulfuric acid were the best catalysts. Reaction with methanol showed greater yields. It was showed very clearly that the presence of water in the reaction medium showed a negative effect in the reaction velocity. Kinetic parameters were estimated and molecular modeling was performed. Protonation of the carboxylic moiety of the fatty acid were defined as rate determinant step for the reaction.

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We have evaluated the influence of alcohol/fatty acid molar ratio (methanol or ethanol), water and catalyst concentrations and temperature by the esterification of palm fatty acids by heterogeneous acid catalysts (varying types, forms, and particle size). Polynaphtalene sulfonic acid (PSA) and niobium oxide (Nb 2 O 5 ) presented better performance than zeolite catalysts. Reaction with methanol presented higher conversion than with ethanol. The experimental design showed that the most relevant variable is the catalyst concentration and all interactions become important in process. A heterogeneous kinetic model was proposed and applied to experimental data. One of the models was adequate for methanol reaction, whereas the homogeneous model was more appropriate for ethanol reaction.

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