For further reading, see Brünger (1991b), Brünger et al. (1986), Brünger et al. (1987), Brünger and Karplus (1991), Clore and Gronenborn (1989,1991), Kaptein et al. (1985), Nilges, Clore, and Gronenborn (1988b,b), Nilges, Gronenborn, and Clore (1989), and Nilsson et al. (1986).
It should be noted that the NOE facility in X-PLOR can be used to restrain any type of distance between selected atoms; e.g., it is possible to restrain the characteristic hydrogen-bonding pattern of secondary structural elements by using the NOE statement.