Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
(A) Stick model of the helical structure of one tetramer (four repeating units) of PS A2. Carbons are colored green, oxygens red, nitrogens blue, and hydrogens white. (B) Electrostatic surface representation of the tetramer. Positive charges are colored blue and negative charges, red. Two grooves are indicated by arrows. Both models are oriented identically, with the left sides tilted slightly toward the observer to make all eight charges visible simultaneously.
