Esterase

About: Esterase is a research topic. Over the lifetime, 7622 publications have been published within this topic receiving 168270 citations.

Cellular basis of ECD brain retention

Abstract: UNLABELLED Clinical observations have shown discrepancies between ECD and HMPAO regional cerebral perfusion, particularly in brain tumors and during stroke recovery. We investigated the nature of the process(es) involved in ECD accumulation in vitro at the cellular level. METHODS Time course incorporation of ECD was studied in a fast-growing human premonocytic line, U937, in a human astrocytic-derived cell line, U373, and a human hybridized endothelial cell line, EaHy926. Cells were further used in experiments aiming to correlate esterase activity and ECD retention. RESULTS Significant differences in ECD retention between these cell lines were observed: %UECD (cpm cells/cpm standard of injected) plateaued within 2 hr in all cases but %UECD was significantly higher in U937 cells (25.1 +/- 3.9% at 120 min) than in the other cell lines (6.1 +/- 0.7% and 8.2 +/- 2.0% at 120 min for U373 and EaHy926, respectively). Contrary to what we expected, total cellular esterase activity (EATOT) was inversely correlated to %UECD.EATOT was 5-fold lower in U937 cells than in U373 and 20-fold lower than in EaHy926. Thus, we compared the membranar to the cytosolic esterase activity of U937 and analyzed the influence of temperature and diisopropylfluorophosphate (DFP, an inhibitor of cytosolic esterase activity) on both ECD retention and enzymatic activities. When cells were exposed to DFP, %UECD was reduced by 80%; while when cells were maintained at 4 degrees C, %UECD continuously increased, corresponding to a passive diffusion since both cytosolic and membranar esterase activities were inhibited. CONCLUSION For optimal uptake of ECD, the membranar fraction of the esterase activity has to be low, while, in contrast, the cytosolic fraction of the esterase activity plays an important role in ECD cell retention. ECD-SPECT is likely able to reflect regional cerebral blood flow in normal and pathological states accurately, but in the event of unusual observations, the membranar esterase activity should be considered to explain reduced ECD retention.

Distinction between 'A'-esterases and arylesterases. Implications for esterase classification.

Abstract: 'A'-esterase activities (substrates paraoxon and pirimiphos-methyloxon) and arylesterase activities (substrate phenyl acetate) were assayed in the sera of 14 species of birds representing seven different orders and 11 species of mammal representing five different orders. Ten species of birds had no detectable 'A'-esterase, and the remaining four species only low activity, yet all birds showed considerable arylesterase activity (16.8-99.3 mumol/min per ml of serum). Ten species of mammal showed both 'A'- and 'aryl'-esterase activities. In humans, gel filtration of serum completely separated peaks representing paraoxonase and arylesterase activities. Thus, in both birds and humans, serum enzymes exist that express arylesterase activity but not 'A'-esterase activity. These findings suggest that a distinction should be made between these two types of esterase in future classifications.

Screening, production and properties of a stereospecific esterase from Pseudomonas sp. S34 with high selectivity to (S)-ketoprofen ethyl ester

Abstract: To isolate novel strains expressing an esterase that hydrolyzed the rac-ketoprofen ethyl ester to (S)-ketoprofen in the stereospecific manner, we screened broad ecological niches and soil samples in which the activity was expected to be found. Thousands of microbial strains were tested to determine their ester-hydrolyzing activity by using an agar plate containing insoluble tributyrin as an indicative substrate, and then further screened by activity on the (R, S)-ketoprofen ethyl ester. Twenty-eight strains were screened primarily and compared with respect to the potential to ketoprofen ethyl ester-hydrolyzing activity in terms of conversion yield and chiral specificity. Consequently, a strain S34 was isolated as a best producer and finally identified as a Pseudomonas sp. S34. We first formulated the optimal medium for the high level production of the enzyme, and as a preliminary experiment for enzymatic resolution, we characterized the fractionated enzyme. The enzyme with ketoprofen ethyl ester-hydrolyzing activity to (S)-ketoprofen showed a high degree of enantioselectivity (>94%) and was mainly found in cell extracts, whereas no distinct activity was detected in culture broth. The optimum pH and temperature of the enzyme were 9.5 and 35 °C, respectively. The activity of the enzyme was markedly increased (four-fold) by addition of a non-ionic detergent Triton X-100 and, resultantly, a high activity toward ketoprofen ethyl ester (52 U/mg) was found. The small-scale conversion of (R, S)-ketoprofen ethyl ester to (S)-ketoprofen using the partially purified enzymes was completed in 28 h, with optical purity of 99% and yield of 47%.