But a very small amount of sulfate was noticed, located between their cell wall and membrane and firmly bound to a small protein. It and transport are repressible by cysteine. Following de-repression and a selective technique for release of periplasmic proteins, crystals were obtained after an only four-fold purification. This ‘binding protein’, is the first of several identified. They are also involved in chemotaxis, as shown by Julius Adler.46