The crystal structure of glycyl‐l‐tyrosine hydrochloride

The crystal structure of glycyl-T.-tyrosine hydrochloride has been determined, making use of the isomorphism of the hydrochloride with the corresponding hydrobromide. Both compounds crystallize with one molecttle of water; space group P2t, two molecules per unit cell. After a direct approximate determination of the [010] and the [001] projection, the atomic coordinates were refined, mainly by consecutive Fourier syntheses of these projections. An essential improvement of the agreement between the calculated and the observed hOl structure factors was obtained by the introduction of an anisotropic temperature factor for the water molecule. The final values for the reliability factor are Rh0z ---0.14 and R~0 = 0-10. The atomic distances are subject ~ a probable error of approximately 0.02 A when both atoms are resolved in the projections; for the other distances this error is estimated to be twice as large. The glycyltyrosine molecule consists of a nearly planar chain, a benzene ring, which is rotated with respect to the plane of the chain, and a c a r b o x y l group , a l m o s t p e r p e n d i c u l a r to t he cha in d i r ec t ion a n d in cis pos i t ion w i t h t h e p e p t i d e carbonyl group. A discussion of the intraand intermoleeular distances is given.