Urine malic acid

The great Swedish chemist C. W. Scheele discovered benzoic acid In gum benzoin In 1775, by sublimation of the resin (16). Applying this technique to many natural materials, between 1770 and 1786, he also discovered tartaric, lactic, oxalic, citric, gallic and malic acids, and In 1776 he found benzoic acid In human urine (16). Following this In 1784, Rouelle (17) found benzoic acid in the urine of cows, but in 1799, Fourcroy and Vauquelin (18) showed that the acid obtained by these workers was not benzoic acid, but another, similar acid, which they could not Identify. 

Malic Acid. Malic acid appears regularly on chromatograms of organic acids of blood (N19) and urine (N20, 05). It can be determined quantitatively by the fluorimetric technique of Hummel (H31), who found values between 0.24 and 0.75 mg% in human whole blood. Much lower values (0.05-0.2 mg%) were found later with the same technique in dog blood plasma (V3). 

Concerning the presence of malic acid in urine, the tubules seem to play a double role they can reabsorb a part of the malate filtered through the glomeruli, and also secrete into the tubular urine malate which has been synthesized within the tubular cells (V3). 

Malic Acids, and 3-Hydroxy-8-alkyl-substituted Dicarboxylic and Tricarboxylic Acid Derivatives in Normal Urine... 

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