Friday, September 26, 2008

EAC Issues Voter’s Guide to Federal Elections

WASHINGTON- The U.S. Election Assistance Commission has issued a guide for citizens about voter registration and voting in the November presidential election. In addition to the basics of ballot-casting, the guide explains special voting procedures, such as early, absentee, and military and overseas voting.

“This guide is a one-stop resource for all types of voters, from first-time voters to frequent voters. It also includes step-by-step instructions for distinct categories of voters, such as military and overseas voters, who must follow special procedures,” said EAC Chair Rosemary Rodriguez.

“Citizens will also learn of new voting options that more states are offering, such as early voting and absentee voting. Voters need to know about all voting options, and this guide shows them how to take advantage of them.”

Since many voting procedures vary from state-to-state, it’s important that citizens always review their state’s materials. Links to all state voter information Web sites are available at, along with any voter guides issued by individual states.

Copies of the EAC’s A Voter’s Guide to Federal Elections have been mailed to every jurisdiction in the country. Election officials may request additional copies at no charge by calling Edgardo Cortés or Juliana Milhofer at (202) 566-3100. An electronic version of the guide is also available online at The EAC Web site also features a variety of information for voters, including registration deadlines for each state, how to register using the National Mail Voter Registration Form, and how to become a poll worker.

Monday, September 15, 2008

Aerobic biodegradation of pollutants

The burgeoning amount of bacterial genomic data provides unparalleled opportunities for understanding the genetic and molecular bases of the degradation of organic pollutants. Aromatic compounds are among the most recalcitrant of these pollutants and lessons can be learned from the recent genomic studies of Burkholderia xenovorans LB400 and Rhodococcus sp. strain RHA1, two of the largest bacterial genomes completely sequenced to date. These studies have helped expand our understanding of bacterial catabolism, non-catabolic physiological adaptation to organic compounds, and the evolution of large bacterial genomes. First, the metabolic pathways from phylogenetically diverse isolates are very similar with respect to overall organization. Thus, as originally noted in pseudomonads, a large number of "peripheral aromatic" pathways funnel a range of natural and xenobiotic compounds into a restricted number of "central aromatic" pathways. Nevertheless, these pathways are genetically organized in genus-specific fashions, as exemplified by the b-ketoadipate and Paa pathways. Comparative genomic studies further reveal that some pathways are more widespread than initially thought. Thus, the Box and Paa pathways illustrate the prevalence of non-oxygenolytic ring-cleavage strategies in aerobic aromatic degradation processes.

Tuesday, September 09, 2008

Ping–pong mechanisms

As shown on the right, enzymes with a ping-pong mechanism can exist in two states, E and a chemically modified form of the enzyme E*; this modified enzyme is known as an intermediate. In such mechanisms, substrate A binds, changes the enzyme to E* by, for example, transferring a chemical group to the active site, and is then released. Only after the first substrate is released can substrate B bind and react with the modified enzyme, regenerating the unmodified E form. When a set of v by [S] curves (fixed A, varying B) from an enzyme with a ping–pong mechanism are plotted in a Lineweaver–Burk plot, a set of parallel lines will be produced.

Enzymes with ping–pong mechanisms include some oxidoreductases such as thioredoxin peroxidase, transferases such as acylneuraminate cytydilyltransferase and serine proteases such as trypsin and chymotrypsin. Serine proteases are a very common and diverse family of enzymes, including digestive enzymes (trypsin, chymotrypsin, and elastase), several enzymes of the blood clotting cascade and many others. In these serine proteases, the E* intermediate is an acyl-enzyme species formed by the attack of an active site serine residue on a peptide bond in a protein substrate. A short animation showing the mechanism of chymotrypsin is linked here.[δ]