Preparation, properties, and uses of two fluorogenic substrates for the detection of 5'-(venom) and 3'-(spleen) nucleotide phosphodiesterases

The synthesis of 5-iodoindoxyl-3-phenylphosphonate and its use in analysis of phosphodiesterase I

5-Iodoindoxyl-3-phenylphosphonate was prepared by using phenylphosphonic dichloride and 5-iodo-1-acetylindoxyl-3-ol. Its physical and chemical properties were studied. The results show that it can be used as an alternative substrate of snake venom phosphodiesterase I for assay of zymogram and in histochemistry.

Alphavirus RNA replicase is located on the cytoplasmic surface of endosomes and lysosomes

Using morphological and cell biological techniques, we have shown that the RNA replicase of Semliki Forest and Sindbis virus (two closely related alphaviruses) is located in complex ribonucleoprotein structures associated with the cytoplasmic surface of modified secondary lysosomes and endosomes. These nucleoprotein complexes often form a bridge between the membrane of the endocytic vacuole and the rough endoplasmic reticulum where the synthesis of the structural proteins of these viruses occurs. The results suggest that these cytopathic vacuoles constitute sites not only for viral RNA synthesis, but also for translation of structural proteins, and for the assembly of nucleocapsids.

Two sensitive, convenient, and widely applicable assays for marker enzyme activities specific to endoplasmic reticulum

Two assay protocols are described for enzyme activities known to reside in the endoplasmic reticulum of a wide variety of species and tissue types, with the intent that they be used as marker enzyme assays in subcellular fractionations. The enzyme activities assayed are choline phosphotransferase and dolichol-P-mannosyl synthase, both of which result in synthesis of lipid products. The assays are constructed to make them easy to perform and sensitive enough to detect enzyme activity even using microgram quantities of cell protein. The assay methodologies are effective not only in vertebrate cells, but in insect cells and yeast cells as well. This implies that these assays should be useful as marker enzyme assays for a wide variety of eukaryotic cells.

Kinetics of intracellular transport and sorting of lysosomal membrane and plasma membrane proteins

We have used monospecific antisera to two lysosomal membrane glycoproteins, lgp120 and a similar protein, lgp110, to compare the biosynthesis and intracellular transport of lysosomal membrane components, plasma membrane proteins, and lysosomal enzymes. In J774 cells and NRK cells, newly synthesized lysosomal membrane and plasma membrane proteins (the IgG1/IgG2b Fc receptor or influenza virus hemagglutinin) were transported through the Golgi apparatus (defined by acquisition of resistance to endo-beta-N-acetylglucosaminidase H) with the same kinetics (t1/2 = 11-14 min). In addition, immunoelectron microscopy of normal rat kidney cells showed that lgp120 and vesicular stomatitis virus G-protein were present in the same Golgi cisternae demonstrating that lysosomal and plasma membrane proteins were not sorted either before or during transport through the Golgi apparatus. To define the site at which sorting occurred, we compared the kinetics of transport of lysosomal and plasma membrane proteins and a lysosomal enzyme to their respective destinations. Newly synthesized proteins were detected in dense lysosomes (lgp's and beta-glucuronidase) or on the cell surface (Fc receptor or hemagglutinin) after the same lag period (20-25 min), and accumulated at their final destinations with similar kinetics (t1/2 = 30-45 min), suggesting that these two lgp's are not transported to the plasma membrane before reaching lysosomes. This was further supported by measurements of the transport of membrane-bound endocytic markers from the cell surface to lysosomes, which exhibited additional lag periods of 5-15 min and half-times of 1.5-2 h. The time required for transport of newly synthesized plasma membrane proteins to the cell surface, and for the transport of plasma membrane markers from the cell surface to lysosomes would appear too long to account for the rapid transport of lgp's from the Golgi apparatus to lysosomes. Thus, the observed kinetics suggest that lysosomal membrane proteins are sorted from plasma membrane proteins at a post-Golgi intracellular site, possibly the trans Golgi network, before their delivery to lysosomes.

Characterization of phosphohydrolase activity in bovine spleen extracts: identification of a bis(p-nitrophenyl)phosphate-hydrolyzing activity (phosphodiesterase IV) which also acts on adenosine triphosphate

Several bovine spleen enzymes with acid pH optima, some of which hydrolyze bis(p-nitrophenyl)phosphate and therefore fit the definition of "phosphodiesterase IV," were partially separated by isoelectric focusing and ion-exchange techniques. The activities were characterized by zymogram analysis with the aid of p-nitrophenyl and 4-methylumbelliferyl phosphate and phosphonate substrates. A number of these enzymes meet the criteria for phosphodiesterase I or other phosphodiesterases. However, the predominant phosphodiesterase I hydrolyzes the bis(p-nitrophenyl)-and 4-methylumbelliferyl phosphates, p-nitrophenyl and 4-methylumbelliferyl phenylphosphonate, and ATP at the beta-gamma bond, but not p-nitrophenyl or 4-methylumbelliferyl 5'-thymidylate (the usual PDE I substrates). These properties, as well as the pH optimum, distinguish the activity from the previously described, alkaline pH optimum PDE I. A second phosphodiesterase hydrolyzes only the phenylphosphonates. Several other activities, less well described, are apparent on zymograms. None of the phosphodiesterases IV was also a phosphodiesterase II (no hydrolysis of 4-methylumbelliferyl 3'-thymidylate).

Flow cytometric DNA and 5'-nucleotide phosphodiesterase in endometrium

One hundred endometrium specimens have been studied with flow cytometry for DNA analysis (FCDA) and a proliferative enzyme marker, 5'-nucleotide phosphodiesterase (5'-NPD). FCDA data showed that aneuploidy was present in only 5 of 40 cancer specimens. However, with corrected histograms, a higher DNA value was observed in the G2/M (6%) of all cancer compared with noncancer specimens (4%). Thus, FCDA can be a useful diagnostic aid for endometrial cancer. The determination of 5'-NPD was done with a quenching method based on the use of 5'-(5-iodo-3-indoxyl)-thymidine phosphodiester as a substrate and 4',6-diamidino-2-phenylindole for DNA. This method could qualitatively define which population of the cell cycle had a higher enzyme level and also quantitatively gave the enzyme units per cell. It was found that 12.5% of all cancer specimens had 5'-NPD activity in the G0/G1 cells and 87.5% in the S and/or G2/M cells, whereas in the noncancer specimens 5'-NPD was found in 28.5% of the G0/G1 cells and 71.5% of the specimens had 5'-NPD in the S and/or G2/M cells. Furthermore, the concentration of 5'-NPD was found to be five times higher in the G2/M cells of the cancer specimens than that in the noncancer specimens. However, in the hyperplasia specimens, the activity was only two times higher in the same cell cycle fraction than in the normal specimens. The results of this investigation provided for the first time evidence that this exonuclease activity alters in the cell cycle fractions and that a decrease in the enzyme activity in G0/G1 cells and an increase in G2/M cells may be a useful marker for neoplastic development in human endometrial cancer.

Tissue specificity of human phosphodiesterase. I. Blood serum

Human blood serum was found to contain two enzymes which hydrolyze various phosphate diester and phosphonate ester bonds. The enzymes were isolated by butanol extraction, ammonium sulfate precipitation, column chromatography and gel electrophoresis. Zymograms showed that one of these enzymes is serum alkaline phosphatase and the other is a 'true' phosphodiesterase I. Serums of 25 persons showed no polymorphisms for either activity. Alkaline phosphatase hydrolyzes phenolic thymidine 5'-nucleotide esters readily, but phenylphosphonate esters very poorly. Serum phosphodiesterase I prefers phenylphosphonate esters to nucleotide diesters, and has no detectable monoesterase activity.

Tissue specificity of human phosphodiesterase. II. Intestinal mucosa

Extracts of human intestinal mucosa were examined for their ability to hydrolyze various phosphodiester, phosphomonoester and phenylphosphonate ester linkages. Enzymes carrying out these reactions were partially purified by butanol extraction, ammonium sulfate precipitation and DEAE-cellulose chromatography, and examined for polymorphism on polyacrylamide gels. Two species of alkaline phosphatase and at least five species of PDE I were identified. Antibodies to purified bovine intestinal phosphatase and phosphodiesterase were found specific for the respective human enzymes.

The synthesis of 4-methylumbelliferyl phenylphosphonate and its used in an improved method for the zymogram analysis of phosphodiesterase I

The 4-methylumbelliferyl analog of p-nitrophenyl phenylphosphonate was prepared and its cleavage by different phosphohydrolases was studied. The new compound, 4-methylumbelliferyl phenylphosphonate, is hydrolyzed by purified phosphodiesterase I (EC 3.1.4.1) from snake venom or bovine intestinal mucosa. This fact has been exploited to develop a zymogram method which allows the detection of these phosphohydrolases on gels, even when the enzymes are present in small amounts in crude extracts. This method is superior to chromogenic methods evolving p-nitrophenol in that it is far more sensitive and is superior to the 4-methylumbelliferyl thymidine 5'-phosphate method in that the substrate is easier to prepare and can be isolated in large quantity.