Differential sorting of lysosomal enzymes in mannose 6-phosphate receptor-deficient fibroblasts.

In higher eukaryotes, the transport of soluble lysosomal enzymes involves the recognition of their mannose 6-phosphate signal by two receptors: the cation-independent mannose 6-phosphate/insulin-like growth factor II receptor (CI-MPR) and the cation-dependent mannose 6-phosphate receptor (CD-MPR). It is not known why these two different proteins are present in most cell types. To investigate their relative function in lysosomal enzyme targeting, we created cell lines that lack either or both MPRs. This was accomplished by mating CD-MPR-deficient mice with Thp mice that carry a CI-MPR deleted allele. Fibroblasts prepared from embryos that lack the two receptors exhibit a massive missorting of multiple lysosomal enzymes and accumulate undigested material in their endocytic compartments. Fibroblasts that lack the CI-MPR, like those lacking the CD-MPR, exhibit a milder phenotype and are only partially impaired in sorting. This demonstrates that both receptors are required for efficient intracellular targeting of lysosomal enzymes. More importantly, comparison of the phosphorylated proteins secreted by the different cell types indicates that the two receptors may interact in vivo with different subgroups of hydrolases. This observation may provide a rational explanation for the existence of two distinct mannose 6-phosphate binding proteins in mammalian cells.     

Ultrastructural localization of the mannose 6-phosphate receptor in rat liver

An affinity-purified rabbit antibody against rat liver mannose 6- phosphate receptor (MP-R) was prepared. The antibody was directed against a 215 kd-polypeptide and it recognized both ligand-occupied and free receptor. Anti-MP-R was used for immunofluorescence and immunoelectron microscopy of cryosections from rat liver. MP-R was demonstrated in all parenchymal liver cells, but not in endothelial lining cells. MP-R labeling was found at the entire plasma membrane, in coated pits and coated vesicles, in the compartment of uncoupling receptor and ligand, and in the Golgi complex. Lysosomes showed only scarce MP-R label. In double-labeling immunoelectron microscopy, MP-R co-localized with albumin in the Golgi cisternae and in secretory vesicles with lipoprotein particles. Cathepsin D was associated with MP- R in the Golgi cisternae. This finding indicates that MP-R/cathepsin D complexes traverse the Golgi complex on their way to the lysosomes. The possible involvement of CURL in lysosomal enzyme targeting is discussed.     

The interaction of phosphorylated oligosaccharides and lysosomal enzymes with bovine liver cation-dependent mannose 6-phosphate receptor

We have analyzed the interaction of phosphorylated oligosaccharides and lysosomal enzymes with immobilized bovine liver cation-dependent mannose-6-P receptor. Oligosaccharides with phosphomonoesters were the only species that interacted with the receptor, and molecules with two phosphomonoesters showed the best binding. Lysosomal enzymes with several oligosaccharides containing only one phosphomonoester had a higher affinity for the receptor than did the isolated oligosaccharides, indicating the possible importance of multivalent interactions between weakly binding ligands and the receptor. The binding of a mixture of phosphorylated lysosomal enzymes to the cation-dependent Man-6-P receptor was markedly influenced by pH. At pH 6.3, almost all of the lysosomal enzymes bound to the receptor; whereas at pH 7.0-7.5, approximately one-third of the material passed through the column, one-third interacted weakly, and one-third bound tightly. The distribution of individual lysosomal enzyme activities was similar to that of the total material. The species of phosphorylated oligosaccharides present on the lysosomal enzymes which interacted poorly with the receptor were similar to those found on the tightly bound material and included species of oligosaccharides with two phosphomonoester groups. Isolated oligosaccharides of this type bound to the receptor over the entire pH range tested. These findings indicate that at neutral pH the phosphorylated oligosaccharides on some lysosomal enzyme molecules are oriented in a manner which makes them inaccessible to the binding site of the cation-dependent Man-6-P receptor. Since the same enzymes bind to the cation-independent Man-6-P receptor at neutral pH, at least a portion of the phosphomannosyl residues must be exposed. We conclude that small variations in the pH of the Golgi compartment where lysosomal enzymes bind to the receptors could potentially modulate the extent of binding to the two receptors.     

Mr 46,000 mannose 6-phosphate specific receptor: its role in targeting of lysosomal enzymes.

Antibodies that block the ligand binding site of the cation-dependent mannose 6-phosphate specific receptor (Mr 46,000 MPR) were used to probe the function of the receptor in transport of lysosomal enzymes. Addition of the antibodies to the medium of Morris hepatoma 7777 cells, which express only the Mr 46,000 MPR, resulted in a decreased intracellular retention and increased secretion of newly synthesized lysosomal enzymes. In fibroblasts and HepG2 cells that express the cation-independent mannose 6-phosphate specific receptor (Mr 215,000 MPR) in addition to the Mr 46,000 MPR, antibodies against the Mr 46,000 MPR inhibited the intracellular retention of newly synthesized lysosomal enzymes only when added to the medium together with antibodies against the Mr 215,000 MPR. Morris hepatoma (M.H.) 7777 did not endocytose lysosomal enzymes, while U937 monocytes, which express both types of MPR, internalized lysosomal enzymes. The uptake was inhibited by antibodies against the Mr 215,000 MPR, but not by antibodies against the Mr 46,000 MPR. These observations suggest that Mr 46,000 MPR mediates transport of endogenous but not endocytosis of exogenous lysosomal enzymes. Internalization of receptor antibodies indicated that the failure to mediate endocytosis of lysosomal enzymes is due to an inability of surface Mr 46,000 MPR to bind ligands rather than its exclusion from the plasma membrane or from internalization.     

Antibody to mannose 6-phosphate specific receptor induces receptor deficiency in human fibroblasts.

Polyclonal antibodies to the mannose 6-phosphate specific receptor from human liver inhibited the endocytosis of lysosomal enzymes in fibroblasts by greater than 95% and enhanced 3-20-fold the secretion of precursors of lysosomal enzymes in these cells. Exposing fibroblasts for 4 h to antibody resulted in loss of greater than 90% of the membrane-bound receptors. If fibroblasts were treated with the antibody in the presence of CBZ-Phe-Ala-CHN2, an inhibitor of lysosomal cysteine proteinases, the receptor and smaller degradation products are recovered in dense lysosomes. In treated cells 18-58% of total receptor-related polypeptides were recovered in dense lysosomes. In control cells less than 4% of the receptor was found in the lysosomal fraction. We conclude from these results that normally the receptor is spared from lysosomal degradation. When tagged with antibody, however, the receptor is transported into lysosomes and degraded. The loss of intracellular receptors involved in segregation of newly synthesized lysosomal enzymes indicates an exchange between the former and the plasma membrane-bound receptors.     

Neither type of mannose 6-phosphate receptor is sufficient for targeting of lysosomal enzymes along intracellular routes

Mouse embryonic fibroblasts that are deficient in the two mannose 6- phosphate receptors (MPRs) MPR 46 and MPR 300 missort the majority (> or = 85%) of soluble lysosomal proteins into the medium. Human MPR 46 and MPR 300 were expressed in these cells to test whether overexpression of a single type of MPR can restore transport of lysosomal proteins to lysosomes. Only a partial correction of the missorting was observed after overexpression of MPR 46. Even at MPR 46 levels that are five times higher than the wild-type level, more than one third of the newly synthesized lysosomal proteins accumulates in the secretions. Two-fold overexpression of MPR 300 completely corrects the missorting of lysosomal enzymes. However, at least one fourth of the lysosomal enzymes are transported along a secretion-recapture pathway that is sensitive to mannose 6-phosphate in medium. In control fibroblasts that express both types of MPR, the secretion-recapture pathway is of minor importance. These results imply that neither overexpression of MPR 46 nor MPR 300 is sufficient for targeting of lysosomal proteins along intracellular routes.     

Transport of surface mannose 6-phosphate receptor to the Golgi complex in cultured human cells

The cation-independent mannose 6-phosphate receptor (MPRCI) functions in the packaging of both newly made and extracellular lysosomal enzymes into lysosomes. The subcellular location of MPRCI reflects these two functions; receptor is found in the Golgi complex, in endosomes, and on the cell surface. To learn about the intracellular pathway followed by surface receptor and to study the relationship between the receptor pools, we examined the entry of the surface MPRCI into Golgi compartments that contain sialyltransferase. Sialic acid was removed from surface-labeled K562 cultured human erythroleukemia cells by neuraminidase treatment. When the cells were returned to culture at 37 degrees C, surface MPRCI was resialylated by the cells with a half-time of 1-2 h. Resialylation was inhibited by reduced temperature, a treatment that allows surface molecules to reach endosomes but blocks further transport. These results indicate that surface MPRCI is transported to the sialyltransferase compartment in the Golgi complex. After culture at 37 degrees C, a small fraction (10-20%) of the resialylated receptor was found on the cell surface. Because a similar fraction of the total receptor pool is found on the cell surface, it is likely that cell surface MPRCI mixes with the cellular pool after resialylation. These data also support the idea that extracellular and newly made lysosomal enzymes are transported to lysosomes through a common compartment.     

Drug-induced phospholipidosis is caused by blockade of mannose 6-phosphate receptor-mediated targeting of lysosomal enzymes

Cationic amphiphilic drugs (CADs) cause massive intracellular accumulation of phospholipids, thereby resulting in phospholipidosis (PLD); however, the molecular mechanism underlying CAD-induced PLD remains to be resolved. Here, we found that treatment of normal rat kidney cells with CADs known to induce PLD caused redistribution of a mannose 6-phosphate/IGF-II receptor (MPR300) from the TGN to endosomes and concomitantly increased the secretion of lysosomal enzymes, resulting in a decline of intracellular lysosomal enzyme levels. These results enable the interpretation of why CADs cause excessive accumulation of undegraded substrates, including phospholipids in lysosomes, and led to the conclusion that the impaired MPR300-mediated sorting system of lysosomal enzymes reflects the general mechanism of CAD-induced PLD. In addition, our findings suggest that the measurement of lysosomal enzyme activity secreted into culture medium is useful as a rapid and convenient in vitro early screening system to predict drugs that can induce PLD.     

Targeted disruption of the mouse cation-dependent mannose 6-phosphate receptor results in partial missorting of multiple lysosomal enzymes.

In mammalian cells two mannose 6-phosphate receptors (MPRs) are involved in lysosomal enzyme transport. To understand the precise function of the cation-dependent mannose 6-phosphate receptor (CD-MPR), one allele of the corresponding gene has been disrupted in mouse embryonic stem cells and homozygous mice lacking this receptor have been generated. The homozygous mice appear normal, suggesting that other targeting mechanisms can partially compensate for the loss of the CD-MPR in vivo. However, homozygous receptor-deficient cells and animals clearly exhibit defects in targeting of multiple lysosomal enzymes when compared with wild-types. Increased levels of phosphorylated lysosomal enzymes were present in body fluids of homozygous animals. In thymocytes from homozygous mice or in primary cultures of fibroblasts from homozygous embryos, there is a marked increase in the amount of phosphorylated lysosomal enzymes that are secreted into the extracellular medium. The cultured fibroblasts have decreased intracellular levels of multiple lysosomal enzymes and accumulate macromolecules within their endosomal/lysosomal system. Taken together, these results clearly indicate that the CD-MPR is required for efficient intracellular targeting of multiple lysosomal enzymes.     

The subcellular localization of soluble and membrane-bound lysosomal enzymes in I-cell fibroblasts: a comparative immunocytochemical study

Using electron microscopic immunocytochemistry with gold probes, we have studied the localization of acid alpha-glucosidase, N-acetyl-beta-hexosaminidase and beta-glucocerebrosidase in cultured skin fibroblasts from control subjects and patients with mucolipidosis II (I-cell disease). In control fibroblasts, a random distribution of acid alpha-glucosidase and N-acetyl-beta-hexosaminidase within the lysosomes was observed, whereas beta-glucocerebrosidase was found to be localized on or near the lysosomal membrane. The observations confirm the soluble character of acid alpha-glucosidase and N-acetyl-beta-hexosaminidase and the membrane-bound character of beta-glucocerebrosidase. In I-cell fibroblasts an abnormal localization of the two soluble enzymes was found. Labeling in lysosomes was very weak, but instead, small 'presumptive' vesicles containing both enzymes were detected throughout the cytoplasm and close to the plasma membrane. These vesicles could be involved in the secretion of the two enzymes. In contrast, a normal membrane-bound lysosomal localization was observed for beta-glucocerebrosidase. It is concluded that the intracellular transport of beta-glucocerebrosidase to the lysosomes can occur even when the mannose-6-phosphate recognition system is defective. This explains the normal activity of beta-glucocerebrosidase in I-cells in contrast to the deficiency of most other lysosomal enzymes.     

Ligand interactions of the cation-dependent mannose 6-phosphate receptor. Comparison with the cation-independent mannose 6-phosphate receptor

The interactions of the bovine cation-dependent mannose 6-phosphate receptor with monovalent and divalent ligands have been studied by equilibrium dialysis. This receptor appears to be a homodimer or a tetramer. Each mole of receptor monomer bound 1.2 mol of the monovalent ligands, mannose 6-phosphate and pentamannose phosphate with Kd values of 8 X 10(-6) M and 6 X 10(-6) M, respectively and 0.5 mol of the divalent ligand, a high mannose oligosaccharide with two phosphomonoesters, with a Kd of 2 X 10(-7) M. When Mn2+ was replaced by EDTA in the dialysis buffer, the Kd for pentamannose phosphate was 2.5 X 10(-5) M. By measuring the affinity of the cation-dependent and cation-independent mannose 6-phosphate receptors for a variety of mannose 6-phosphate analogs, we conclude that the 6-phosphate and the 2-hydroxyl of mannose 6-phosphate each contribute approximately 4-5 kcal/mol of Gibb's free energy to the binding reaction. Neither receptor appears to interact substantially with the anomeric oxygen of mannose 6-phosphate. The receptors differ in that the cation-dependent receptor displays no detectable affinity for N-acetylglucosamine 1'-(alpha-D-methylmannopyranose 6-monophosphate) whereas this ligand binds to the cation-independent receptor with a poor, but readily measurable Kd of about 0.1 mM. The spacing of the mannose 6-phosphate-binding sites relative to each other may also differ for the two receptors.     

The lysosomal trafficking of acid sphingomyelinase is mediated by sortilin and mannose 6-phosphate receptor

Acid sphingomyelinase (ASM), a member of the saposin-like protein (SAPLIP) family, is a lysosomal hydrolase that converts sphingomyelin to ceramide. Deficiency of ASM causes a variant form of Niemann-Pick disease. The mechanism of lysosomal targeting of ASM is poorly known. Previous studies suggest that ASM could use in part the mannose 6-phosphate receptor (M6P-Rc). Sortilin, a type I transmembrane glycoprotein that belongs to a novel family of receptor proteins, presents structural features of receptors involved in lysosomal targeting. In this study we examined the hypothesis that sortilin may be implicated in the trafficking of ASM to the lysosomes. Using a dominant-negative sortilin construct lacking the cytoplasmic tail, which is essential to recruit adaptor proteins and clathrin, we demonstrated that sortilin is also involved in the lysosomal targeting of ASM. Confocal microscopy revealed that truncated sortilin partially inhibited the lysosomal trafficking of ASM in COS-7 cells and abolished the lysosomal targeting of ASM in I-cells. Pulse-chase experiments corroborated that sortilin is involved in normal sorting of newly synthesized ASM. Furthermore, over-expression of truncated sortilin accelerated and enhanced the secretion of ASM from COS-7 cells and I-cells. Co-immunoprecipitation assays confirmed the interaction between sortilin and ASM. In conclusion, ASM uses sortilin as an alternative receptor to be targeted to the lysosomes.     

Biosynthesis and endocytosis of lysosomal enzymes in human colon carcinoma SW 1116 cells: impaired internalization of plasma membrane-associated cation-independent mannose 6-phosphate receptor.

The human colon adenocarcinoma cell lines SW 948, SW 1116, and SW 1222 were tested for their ability to sort and internalize lysosomal enzymes. The biosynthesis of the lysosomal enzymes cathepsin B, arylsulfatase A, and beta-hexosaminidase in these cell lines exhibits no significant differences to that in human fibroblasts. The intracellular targeting of newly synthesized hydrolases to the lysosomes relies in colon carcinoma cells on the mannose 6-phosphate receptor system. Both the cation-independent mannose 6-phosphate receptor (CI-MPR) and the cation-dependent mannose 6-phosphate receptor are expressed in all colon carcinoma cell lines investigated. Endocytosis of lysosomal enzymes via mannose 6-phosphate receptors is reduced in colon carcinoma cells as compared with human fibroblasts. SW 1116 cells were shown to be deficient in receptor-mediated endocytosis of mannose 6-phosphate containing ligands. Ligands of other endocytic receptors as well as the fluid-phase marker horseradish peroxidase were internalized at normal rates. While antibodies against CI-MPR bind to the surface of SW 1116 cells, these antibodies cannot be internalized. These data suggest that the cycling of CI-MPR is specifically impaired in SW 1116 cells.     

Plasmalemmal vesicles are involved in transendothelial transport of albumin, lysosomal enzymes and mannose 6-phosphate receptor fragments in capillary endothelium

With the use of immunoelectron microscopy we have demonstrated the presence of lysosomal enzymes (acid alpha-glucosidase and glucocerebrosidase) and fragments of the 270 kDa receptor for mannose 6-phosphate and insulin-like growth factor II in blood plasma, plasmalemmal vesicles of endothelial cells and pericapillary spaces in human skeletal muscle tissue. At these locations, the three proteins colocalized with albumin known to be transported from the capillaries into the pericapillary spaces. Immunoblot analysis of plasma revealed the presence of relatively high molecular weight polypeptides in this material. These observations strongly suggest that high molecular weight species of lysosomal enzymes can pass the endothelial barrier in skeletal muscle tissue.     

46 kd mannose 6-phosphate receptor: cloning, expression, and homology to the 215 kd mannose 6-phosphate receptor

We have isolated cDNA clones encoding the entire sequence of the bovine 46 kd cation-dependent mannose 6-phosphate (CD Man-6-P) receptor. Translation of CD Man-6-P receptor mRNA in Xenopus laevis oocytes results in a protein that binds specifically to phosphomannan-Sepharose, thus demonstrating that our cDNA clones encode a functional receptor. The deduced 279 amino acid sequence reveals a single polypeptide chain that contains a putative signal sequence and a transmembrane domain. Trypsin digestion of microsomal membranes containing the receptor and the location of the five potential N-linked glycosylation sites indicate that the receptor is a transmembrane protein with an extracytoplasmic amino terminus. This extracytoplasmic domain is homologous to the approximately 145 amino acid long repeating domains present in the 215 kd cation-independent Man-6-P receptor.     

Effect of 2-deoxyglucose on lysosomal enzymes in cultured human skin fibroblasts

Addition of 2-deoxyglucose, an inhibitor of glycosylation of proteins, to the medium of confluent cultures of human skin fibroblasts prevents the increase in specific activity of lysosomal enzymes that normally occurs after confluence. Maximal inhibition is obtained at a concentration of about 1 mM 2-deoxyglucose. The inhibition by 2-deoxyglucose is reversible. The K_m, pH dependence and electrophoretic mobility of the acid hydrolases tested was the same in cells cultured with or without 2-deoxyglucose. In homogenates of cultured human skin fibroblasts, about 95% of the β-hexosaminidase and α-galactosidase activity and about 65 % of the acid phosphatase activity with β-glycerolphosphate as substrate binds to concanavalin A (ConA); 2-deoxyglucose affects only the activity able to bind to ConA. In cells cultured in the presence of 2-deoxyglucose, the specific activity of alkaline phosphodiesterase I, a plasma membrane glycoprotein is lowered. 2-Deoxyglucose has no effect on the specific activity of succinate dehydrogenase, lactate dehydrogenase or total cellular protein.     

Distinctive regulation of the functional linkage between the human cation-independent mannose 6-phosphate receptor and GTP-binding proteins by insulin-like growth factor II and mannose 6-phosphate

The rat insulin-like growth factor II (IGF-II) receptor develops transmembrane signaling functions by directly coupling to a guanine nucleotide-binding protein (G protein) having a 40-kDa alpha subunit, Gi-2, whereas recent studies have indicated that the IGF-II receptor is a molecule identical to the cation-independent mannose 6-phosphate receptor (CI-MPR), a receptor implicated in lysosomal enzyme sorting. In this study, by using vesicles reconstituted with the clonal human CI-MPR and G proteins, we indicated that the CI-MPR could stimulate guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) binding and GTPase activities of Gi proteins in response to IGF-II. The stimulatory effect of IGF-II on Gi-2 depended on the reconstituted amount of the CI-MPR; it could not be found in vesicles reconstituted with Gi-2 alone; and it was also observed on Gi-1 reconstituted with the CI-MPR in phospholipid vesicles. Of interest, such stimulatory effect was not reproduced by Man-6-P in CI-MPR vesicles reconstituted with either G protein. Furthermore, the affinity for Man-6-P-mediated beta-glucuronidase binding to several kinds of native cell membranes was not reduced by 100 microM GTP gamma S. Instead, however, Man-6-P dose-dependently inhibited IGF-II-induced Gi-2 activation with an IC50 of 6 microM in vesicles reconstituted with the CI-MPR and Gi-2. The action of 100 nM IGF-II was completely abolished by 1 mM Man-6-P. Such an inhibitory effect of Man-6-P was reproduced by 4000 times lower concentrations of beta-glucuronidase or similar concentrations of fructose 1-phosphate, but not by mannose or glucose 6-phosphate. These results indicate that the human CI-MPR has two distinct signaling functions that positively or negatively regulate the activity of Gi-2 in response to the binding of IGF-II or Man-6-P.     

Recognition of Dictyostelium discoideum lysosomal enzymes is conferred by the amino-terminal carbohydrate binding site of the insulin-like growth factor II/mannose 6-phosphate receptor

The insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/MPR) is a type I glycoprotein that mediates both the intracellular sorting of lysosomal enzymes bearing mannose 6-phosphate (Man-6-P) residues to the lysosome and the bioavailability of IGF-II. The extracytoplasmic region of the IGF-II/MPR contains 15 repeating domains; the two carbohydrate recognition domains (CRDs) have been localized to domains 1-3 and 7-9, and the high-affinity IGF-II binding site maps to domain 11. To characterize the carbohydrate binding properties of the IGF-II/MPR, regions of the receptor encompassing the individual CRDs were produced in a baculovirus expression system. Characterization of the recombinant proteins revealed that the pH optimum for carbohydrate binding is significantly more acidic for the carboxyl-terminal CRD than for the amino-terminal CRD (i.e., pH 6.4-6.5 vs 6.9). Equilibrium binding studies demonstrated that the two CRDs exhibit a similar affinity for Man-6-P. Furthermore, substitution of the conserved arginine residue in domain 3 (R435) or in domain 9 (R1334) with alanine resulted in a similar >1000-fold decrease in the affinity for the lysosomal enzyme, beta-glucuronidase. In contrast, the two CRDs differ dramatically in their ability to recognize the distinctive modifications (i.e., mannose 6-sulfate and Man-6-P methyl ester) found on Dictyostelium discoideum lysosomal enzymes: the amino-terminal CRD binds mannose 6-sulfate and Man-6-P methyl ester with a 14-55-fold higher affinity than the carboxyl-terminal CRD. Taken together, these results demonstrate that the IGF-II/MPR contains two functionally distinct CRDs.     

Ultrastructural localization of lysosomal enzymes in the egg cortex of Brachydanio

The localization of acid phosphatase (E.C. 3.1.3.2), inorganic trimetaphosphatase (E.C. 3.6.1.2), and aryl sulfatase (E.C. 3.1.6.1) in the cortex of unactivated and activated eggs of Brachydanio was examined by ultrastructural cytochemistry. Using a lead capture method, activity for all three acid hydrolases was demonstrated in organelles of the cortex before and after egg activation. Acid phosphatase (AcPase) reaction product was consistently present in primary lysosomes, secondary lysosomes, multivesicular bodies, and yolk bodies. AcPase activity was absent from mitochondria, profiles of the endoplasmic reticulum, coated pits of exocytosed cortical granules, and coated vesicles. Although most cortical granules of the mature, unactivated egg were unreactive for this enzyme, a few showed AcPase reaction product. It is not clear whether the AcPase-positive granules might be an immature form of cortical granules or a subpopulation of these organelles with lysosomal properties. Most cisternae of the Golgi apparatus did not stain for AcPase; however, reaction product was occasionally localized in a single cisterna as well as several small vesicles at the inner face of the Golgi. The intensity of the reaction product and the pattern of distribution of trimetaphosphatase (Tm-Pase) activity was very similar to that of AcPase. However, TmPase was never observed in cortical granules. Cortices of unactivated and activated eggs showed less overall aryl sulfatase (ArSase) activity when compared with AcPase and TmPase. The presence of ArSase reaction product in lysosomes and multivesicular bodies confirmed the acid hydrolytic nature of these organelles. AcPase and TmPase, and to a lesser extent ArSase, are adequate markers of a cortical lysosomal system in the danio egg.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition by lysosomal enzymes and mannose-6-phosphate of the phosphorylation of the lysosomal enzyme binding receptor protein from monkey brain

The lysosomal enzymes beta-glucuronidase and alpha-L-fucosidase and mannose-6-phosphate inhibited the phosphorylation of the lysosomal enzyme binding receptor protein prepared from monkey brain. Inhibition of both serine and tyrosine phosphorylation was observed. A non-lysosomal glycoprotein enzyme butyrylcholinesterase, mannose or glucose did not inhibit phosphorylation. Tyrosine phosphorylation of histone by the receptor protein was also inhibited by the lysosomal enzymes and mannose-6-phosphate.