Figure 5.

Portion of the ¹H–¹⁵N HSQC 800 MHz cryo-probe spectrum of the same pooled human serum shown in Figure 4. Proteins are removed by ultrafiltration using a 3 kDa molecular weight cutoff filter and carboxyl group containing metabolites tagged with ¹⁵N-cholamine. The peak enclosed within the square box is missing in the protein precipitated serum (see Figure 4). Identified metabolites: 3, alanine; 6, asparagine; 7, aspartic acid; 8, betaine; 9, citric acid; 12, formic acid; 15, glutamic acid; 17, glycine; 20, histidine; 21, 3-hydroxybutyric acid; 22, 4-hydroxyproline; 23, 2-hydroxyisobutyric acid; 25, isoleucine; 28, lactic acid; 31, maleic acid; 33, malonic acid; 39, propionic acid; 48, valine.