Spontaneously formed sugar polymers have long been recognized as important components of soil (as humins) and cooked foods (as melanoidin products of non-enzymatic browning). More recently, it has been suggested that they were also important in the advent of life on earth because they form micro-spherules that can encapsulate reactions, potentially acting as precursors of modern cells. However, the molecular structures of these polymers has been difficult to determine because of their amorphous and insoluble nature. All that was clear is that they contain aromatic rings that include oxygen (furans) and nitrogen (pyrroles). The further supposition was that these rings were directly linked in chains. Now, using solid state NMR, Professor Judith Herzfeld, undergraduate Danielle Rand, graduate students Melody Mak-Jurkauskas and Irena Mamajanov, and postdoctoral research associates Yoh Matsuki and Eugenio Daviso, have shown that the polymer is much more complicated, with the aromatic rings cross-linked by variously dehydrated sugar molecules. Their paper, entitled “Molecular Structure of Humin and Melanoidin via Solid State NMR“, appeared online on April 1 in Journal of Physical Chemisty B.
Spring-loading the active site of cytochrome P450
Enzymes differ from other catalysts in the exceptional substrate selectivity they exhibit. However, the active sites of related enzymes are often very similar, even though different substrates are acted upon (for example in the superfamily of cytochrome P450s). How does a given enzyme preferentially bind a particular substrate? In a new paper appearing in the jounal Metallomics, Chemistry grad student Marina Dang and Profs. Susan Sondej Pochapsky and Thomas Pochapsky use nuclear magnetic resonance (NMR) to identify a helical structure remote from the active site of the enzyme cytochrome P450cam that is responsive to changes in substrate. They propose that this helix can adjust the position of residues that contact substrate in the enzyme active site, much like the spring that holds batteries in place against electrical contacts in a flashlight.
