beta-Glucuronidase is transported slowly to lysosomes in BW5147 mouse lymphoma cells: evidence that the prelysosomal enzyme is not restricted to the endoplasmic reticulum

Identification and androgen regulation of egasyn in the mouse epididymis

The expression and androgen regulation of egasyn, the endoplasmic reticulum-targeting protein of beta-D-glucuronidase, was examined in the mouse-epididymis. The proximal (caput) and distal (corpus & cauda) epididymal tissue extracts were prepared by homogenization and sonication in buffered Triton X-100 solution, and high speed centrifugation. The supernatant when resolved by 2D-PAGE under non-denaturing conditions and stained for esterase activity showed that the distal (but not proximal) epididymis of the normal mouse contain several specific forms of esterases. These forms include a series of four variants (pI 5.2-5.75) with high mobility (HM) and esterase activity, and three faintly staining variants (beginning at pI 6.0) with low mobility (LM). Several lines of evidence indicate that the specific esterases seen in the corpus/cauda epididymidis are egasyn-esterases. Firstly, these molecular forms were not seen in the distal epididymal extracts from the egasyn-deficient mouse. Secondly, the HM forms can be immunoprecipitated with anti-egasyn antibody, suggesting the presence of free egasyn. Finally, the LM forms disappeared after heat treatment (56 degrees C for 8 min), a condition known to dissociate egasyn:beta-D-glucuronidase complex. This result indicates that a small amount of egasyn is complexed with beta-D-glucuronidase. Immunoblotting (Western blot) studies (using anti-egasyn antibody) following resolution of egasyn released from the egasyn:beta-D-glucuronidase complex revealed a single band of an apparent molecular weight 64 kDa in the distal (but not proximal) epididymis, indicating that the mouse epididymal egasyn is identical or very similar to the liver egasyn. Castration of mice lead to the appearance of free and complexed egasyn forms in the proximal epididymis. Testosterone supplementation to the castrated mice resulted in the disappearance of the induced egasyn forms from the caput epididymidis. Taken together, these results indicate that the expression of egasyn in the epididymis is region-specific and is differentially regulated by androgens.

A fluorogenic substrate for beta-glucuronidase: applications in fluorometric, polyacrylamide gel and histochemical assays

We have developed a fluorogenic substrate, ELF-97 beta-D-glucuronide, that provides significant advantages over existing substrates in detecting beta-glucuronidase activity. ELF-97 beta-D-glucuronide allows the detection of enzymatic activity in situ, yielding a hydrolytic product that exhibits maximal fluorescence within the physiological pH range. This substrate yields a hydrolytic product that demonstrates a more than 100 nm Stokes shift, which minimizes interference from autofluorescence in plant tissue. With the commercial enzyme, ELF-97 beta-D-glucuronide can detect less than 2 x 10(-4) U/ml of beta-glucuronidase activity in solution, and 5 x 10(-4) U per lane in polyacrylamide gels. Assays using transgenic Arabidopsis, whole leaf extracts of GUS-positive, but not GUS-negative plans, show significant GUS activity upon incubation with ELF-97 beta-D-glucuronide. Furthermore, the ability of this substrate to form insoluble precipitates at the sites of enzymatic activity makes it suitable for in situ localization of GUS activity in tissue samples of higher plants.