1. 17) Obtained from Cambridge Isotope Laboratories, contained: alanine (7.3%), arginine (6.8%), asparatic acid (9.5%), glutamic acid (10.4%), glycine (6.2%), histidine (1.9%), isoleucine (4.0%), leucine (10.6%), lysine (13.7%), methionine (1.0%), phenylalanine (4.5%), proline (6.5%), serine (4.1%), threonine (4.6%), tyrosine (3.9%) and valine (5.1%). 500 mg of this mixture ofL-[U-13C]amino acids was dissolved in 1 liter of the medium.
2. 19) A clear1JC5–C1′=69.5 Hz was visible, but C1′ was not labelled. However, given the high incorporation rate at C5, approximately 30% of13C at C1′ had a13C at C5 as a neighbour. Due to the close proximity of the signals to one another, the1Jand2Jcoupling of C2, C3 and C4 cannot be unambiguously assigned.