Lactic acid and protein interactions: implications for the NMR visibility of lactate in biological systems

The addition of bovine serum albumin (BSA) to a solution of lactate and ala nine resulted in the disappearance of the H-1-NMR resonances from lactate b ut not alanine. As temperature is increased lactate becomes increasingly NM R visible and after heating above 65 degrees C and cooling to 25 degrees C lactate binding is reduced. With a concentration of 0.2 mM BSA, there was a linear relationship between NMR visible lactate versus total lactate over a range of lactate concentrations of 0.2-35 mM (slope 0.384 +/- 0.003) indi cating that approx. 60% of the added lactate is not visible in the H-1-NMR spectrum. With a 0.1 mM BSA solution, however, the slope was markedly highe r indicating that under these conditions only 25-30% of the lactate was NMR invisible. The results from this study indicate that decreased NMR visibil ity of lactate in proteinaceous solutions is due to non-specific binding wh ich is dependent on the tertiary structure of the protein. This has importa nt implications not only for the interpretation of in vivo H-1-NMR experime nts but also for C-13, and C-14 studies of metabolism. (C) 1999 Elsevier Sc ience B.V. All rights reserved.