Metabolism as a production line

Metabolic pathways might be smarter than we think, according to Alon Zaslaver, Uri Alon (Weizmann Institute, Rehovot, Israel), and colleagues. At least in bacterial amino acid biosynthesis pathways, the production schedules are designed using two principles that, according to theory, optimize the pathways for the fastest output using the least amount of enzymes.

“If the cell had an infinite amount of energy it would just dump very high levels of all these proteins together right away,” says Alon. “But bacteria are limited by protein synthesis. In this economy they need to make tradeoffs.”

Alon's group investigated the tradeoffs using 52 gene fusions to fluorescent proteins. They found that genes encoding early steps in a pathway are turned on both earlier and more aggressively, thus ensuring that later gene products have a sufficiently high concentration of substrate...