Biochemical analysis of arginase and ornithine carbamoyltransferase in human vitreous humor

Background. The presence of arginase and ornithine carbamoyltransferase (OT C'ase) enzymes in human vitreous humor after death was investigated in this study. To the best of our knowledge, there is no prior report on the activ ity of arginase or ornithine carbamoyltransferase in human vitreous humor. Methods. The presence of arginase and OTC'ase activities were examined in t he human vitreous humor of 19 samples. Spectrophotometric methods were used to determine activities of arginase and OTC'ase. Results. Arginase activity was detected in human vitreous humor, whereas OT C'ase activity was below the detection limit. Therefore, we focused on bioc hemical analysis of arginase in human vitreous humor. Kinetic properties of arginase activity in vitreous humor were optimized. In contrast to other a rginases, optimal preincubation temperature and pH were 40 degreesC and 8.8 , respectively. Km of vitreous arginase for L-arginine was 6 mm. Preincubat ion of the enzyme with Mn2+ ions caused a significant increase (33%) in arg inase activity. Conclusions. The activity and presence of arginase as well as its kinetics in human vitreous are documented in this study. Biochemical functions and t he importance of arginase in vitreous humor are not well understood. Howeve r. its presence may be explained by means of its involvement in polyamine b iosynthesis as observed in the other extrahepatic tissues. (C) 2001 IMSS. P ublished by Elsevier Science Inc.