A method for enzymatic determination of citrate in serum and urine

A method for determination of citrate in serum and urine using citrate lyase is described. The influence of pH, zinc, magnesium, and calcium ions on the reaction velocity is studied. Citrate lyase activity is found rather insensitive to variations in pH round the pH-optimum at 8.2. Zinc ions activate the reactions. The optimal concentration of zinc ions in the reaction mixture is found to depend on the calcium concentration of samples. Perchloric acid is used for precipitation of proteins. The perchloric ion inhibits the reaction, and a procedure for removing perchlorate is given. Sensitivity of analysis is 0.005 mmo1/1 for serum and urine samples, respectively. No contamination of citrate lyase is found, and therefore addition of lactate dehydrogenase is considered unneccessary.