Lactacidogen

LACTACIDOGEN, a compound containing hexose and phosphoric acid, found in muscles and discovered by Embden (1912). It is now established that it is hexosemonophosphoric acid (C₆H₁₁O₅·H₂PO₄) and not hexosediphosphoric acid, as was previously believed. Since L. rotates the plane of polarization to the right, it must be assumed that it is glucosomonophosphoric acid. Properties of L. Free hexosemonophosphoric acid is a syrupy liquid; its aqueous solution has a strongly acid reaction to litmus. L. reduces Fehling's solution and possesses many properties of hexoses. It is quantitatively precipitated by copper sulfate and lime water. With brucine, L. forms a well-crystallizing salt; L. is usually isolated from muscles in the form of this salt (or barium salt) (it is most convenient to use rabbit muscles). Physiol. role of lactacidogen. L. is an intermediate product in carbohydrate metabolism in muscles. Glucose formed from the breakdown of glycogen first combines with phosphoric acid to form L., which then splits into phosphoric acid and active hexose, with the further transformation of which lactic acid is formed, etc. In his work to clarify the role of L., Embden used a method for determining L. based on determining the amount of phosphoric acid cleaved during a two-hour autolysis of minced muscles in a 2% solution of sodium bicarbonate at 30-40°, assuming that under these conditions phosphoric acid is cleaved only from L. But Lohmann (1928) showed that under these conditions pyrophosphoric acid present in muscles also splits (muscles also contain other phosphoric acid compounds, such as phosphocreatine, adenylic acid). On the other hand, Embden and Jost found that under the above conditions not all hexose-phosphoric acid splits. This made it necessary to verify Embden's data using a new method that would determine the true content of L. Such a method was proposed by Embden and Jost in 1928 (see below). Recent research has confirmed the fact previously established by Embden that L. splits at the moment of muscle contraction; during relaxation the reverse synthesis of L. occurs. The breakdown and synthesis of L. are enzymatic processes; according to some authors, these two processes are catalyzed by one enzyme, according to others by two: namely, phosphatase and phosphatase (Euler, Meyerhof). (See also Glycolysis, Hexosephosphoric acids.) White muscles are richer in L. than red muscles. Whether hexosediphosphoric acid is present in muscles along with hexosemonophosphoric acid has not yet been clarified. L. is found in both striated and smooth muscles, as well as in other organs (in the brain, kidneys). Muscles and organs Muscles white striated ........ Muscles red striated........ Muscles smooth Lactacidogen, expressed as hexose from 0.112% to 0.146% » 0.074% » 0.106% 0.049% » 0.071% Brain ............. » 0.030% » 0.085% Quantitative determination of L. in muscles and other organs by the method of Embden and Jost: in an extract (e.g., from muscles), freed from proteins, all L. is precipitated by alcohol containing ammonia in the presence of an excess of magnesium ions; other reducing substances remain in the solution. The precipitate is washed, dried, and then dissolved in dilute HCl. The reducing power of this solution is determined by the method of Hagedorn and Jensen, and from this the amount of lactacidogen is calculated.