Nonequilibrium of two redox couplets in human plasma: lactate-pyruvate and beta-hydroxybutyrate-acetoacetate.
We examined the extracellular equilibrium status of two redox couplets normally found in plasma (lactate-pyruvate [L-P], beta-hydroxybutyrate, and acetoacetate) during acute metabolic acidosis produced by muscle exertion. Both pre- and postexertion plasma spontaneously underwent loss of acetoacetate and gain of L when compared to the baseline values. Exercise further induced a 332% rise in L (p less than .001) and a 102% rise in P (p less than .001). The empirically derived ratio of equilibrium constants, KLP/KBA, fell 50% (p less than .001), and the calculated change in free energy (delta F) fell from 3.6 to 3.1 kcal/mol (p less than .001) after exercise. The changes induced by exertion were simulated closely by an in vitro model of a reduced state. Thus, the triad of inconstant metabolite concentrations, inconstant KLP/KBA, and delta F both inconstant and non-zero, indicates that there is no state of equilibrium for these metabolite couplets in human plasma. The KLP/KBA ratio appeared to reflect the degree of deviation from equilibrium and may therefore be useful when investigating altered redox states such as metabolic acidosis.
D020155:3-Hydroxybutyric Acid; D000090:Acetoacetates / Q000097:blood*; D000138:Acidosis / Q000378:metabolism; D000328:Adult; D005260:Female; D006801:Humans; D006885:Hydroxybutyrates / Q000097:blood* / Q000378:metabolism; D007773:Lactates / Q000097:blood* / Q000378:metabolism; D008297:Male; D009243:NAD / Q000097:blood / Q000378:metabolism; D010084:Oxidation-Reduction; D005082:Physical Exertion; D011773:Pyruvates / Q000097:blood* / Q000378:metabolism
D000090:Acetoacetates; D006885:Hydroxybutyrates; D007773:Lactates; D011773:Pyruvates; D009243:NAD; C016635:acetoacetic acid; D020155:3-Hydroxybutyric Acid