Different effects of sulfur amino acids on prolidase and prolinase activity in normal and prolidase-deficient human erythrocytes

BackgroundProlidase and prolinase activity is known to be enhanced significantly in some diseases. Recently, the effect of amino acids on prolidase and prolinase activity in normal and prolidase-deficient human erythrocytes was investigated. It was reported that both enzymes were enhanced by glycine and alanine in the presence of MnCl2.MethodsErythrocytes were isolated from heparinized blood from normal human and a patient with prolidase deficiency. Effects of various sulfur amino acids on prolidase and prolinase activities against iminodipeptides in the presence of 1 or 0.1 mmol/l MnCl2 were investigated.ResultsProlinase activity against prolylglycine in normal and prolidase-deficient erythrocyte lysates was inhibited by l-methionine, NAc-l-methionine and d,l-methionine in a concentration-dependent manner, but d-methionine enhanced the activity in low concentrations (0–20 mmol/l). d,l-Homocysteine inhibited the activity more strongly than other sulfur amino acids tested in a concentration-dependent manner. On the other hand, prolidase activity against glycylproline was enhanced by l-methionine, d-methionine, d,l-methionine, d,l-homocysteine thiolactone and d,l-ethionine. The rates of enhancement by these sulfur amino acids were in the following order: d,l-ethionine > d,l-methionine, d-methionine, d,l-homocysteine thiolactone > l-methionine (10 mmol/l).ConclusionThe prolinase activity in normal and prolidase-deficient erythrocyte lysates was inhibited by l-methionine, d,l-ethionine and d,l-homocysteine. On the other hand, prolidase activity in their erythrocyte lysates was enhanced by d,l-ethionine, d-methionine and l-methionine. These results indicate the effects of these sulfur amino acids on prolidase and prolinase activities were different.