Degradation of polysaccharides, mucopolysaccharides, and glycoproteins by lysosomal glycosidases

Design of Polyamine-Grafted Starches for Nucleotide Analogue Delivery: In Vitro Evaluation of the Anticancer Activity

Nucleotide analogues are a therapeutic class that is very promising and currently used in clinics, notably against viral infectious diseases and cancer. However, their therapeutic potential is often restricted by a poor stability in vivo, the induction of severe side effects, and limited passive intracellular diffusion due to their hydrophilicity. Polysaccharide-based polymers (e.g., starch) have considerable advantages, including a lack of toxicity and the absence of antigenicity. The aim of this study was to develop new cationic starches able to form complexes with nucleotide analogues, thus protecting them and increasing their cell uptake. At the same time, the material should demonstrate good biocompatibility and low cytotoxicity. Different polyamines, (TREN, TEPA, and spermine) were grafted to starch to evaluate the impact of side-chain properties. The resulting cationic starch derivatives were characterized (e.g., degree of modification) and compared in their ability to form polyplexes with ATP as a model nucleotide. Among the tested candidates, the formulation of starch-TEPA and ATP with an N/P ratio of 2 led to nanoparticles with a size of 429 nm, a PdI of 0.054, and a ζ potential of -9 mV. MTT and LDH assays on A549 cell line showed low toxicity for this polymer. Confocal microscopy study proved that the cell internalization was an incubation-time- and energy-dependent process. Most important, starch-TEPA complexed with ddGTP showed significant biological activity on A549 cancer cells compared to that of plain ddGTP at the same concentration.

Preparation of nanosized coacervates of positive and negative starch derivatives intended for pulmonary delivery of proteins

Use of charged starch-derivatives as nanoscaled protein carriers and their in vitro evaluation.

Urinary N-acetyl beta glucosaminidase and gamma glutamyl transferase as early markers of diabetic nephropathy

Albumin and enzymes-N-acetyl-beta-glucosaminidase (NAG) and gamma glutamyl transferase (GGT) were estimated in the morning random urine samples of 196 albustix negative diabetic patients to evaluate the clinical utility of these urinary enzymes as early markers of diabetic nephropathy. Albumin was estimated by immunoturbidimetric method and enzymes by linetic essay within six hours of voiding of urine. The urinary albumin and urinary enzyme concentration was calculated in terms of ratio with respect to urinary creatinine. Correlation coefficient (r) bewween urinary albumin and urinary enzymes in normoalbuminuric, microalbuminuric and overall diabetic cases was 0.23, 0.32 and 0.40 respectively for NAG, and 0.08, 0.06 and 0.18 respectively for GGT. NAG excretion was found increased in 34%, 63.7% and 49.5% of normoalbuminuric, microalbuminuric and overall diabetic cases respectively while GGT in 6.4%, 24.5% and 15.8%. The correlation coefficient between urinary albumin and NAG in normoalbuminuric, microalbuminuric, and overall diabetic patients with increased NAG excretion was found only 0.31, 0.27 and 0.35 respectively. No correlation was found between duration of diabetes and enzyme excretion. The study suggests that urinary NAG or GGT or both together do not have any clinical significance as an early marker of diabetic nephropathy.

Increased urinary N-acetyl-beta-glucosaminidase (NAG) excretion in young insulin-dependent diabetic patients

We evaluated urinary N-acetyl-beta-glucosaminidase (NAG) excretion in overnight and in second morning urine in 50 young diabetic patients, aged 7.4-25 years with a disease duration from 2-19.6 years. In all patients we evaluated urinary NAG and creatinine excretion, in both overnight and second morning urine, glycosuria, fasting blood glucose and HbA1c levels, insulin requirement, blood pressure, and the presence of microangiopathic complications. Urinary NAG excretion was also evaluated in 69 age- and sex-matched controls. NAG was determined using 3-cresolsulfonphtaleinyl-beta-N-acetylglucosaminide as substrate (Boehringer Mannheim, Germany). In the diabetic patients NAG/Cre ratios were significantly higher than in controls both in overnight and second morning urine (P < 0.0005, respectively). We observed significantly higher NAG/Cre ratio levels in the second morning than in overnight urine, both in controls and in diabetics (P < 0.0005, respectively). Elevated (above 2 S.D. of the mean) NAG/Cre ratios were found in 17/50 patients (34%) in overnight urine and in 29/50 (58%) in second morning urine. No correlation was observed between NAG/Cre ratio levels and age, duration of disease, pubertal stage, body mass index, fasting blood glucose, glycosuria, insulin requirement and blood pressure. The patients with one or more complications did show NAG/Cre ratio levels significantly higher than those without complications (P < 0.005) in second morning urine, but not in overnight urine. Our study has demonstrated an increased rate of urinary NAG excretion in young IDDM patients, in particular in those with microangiopathic complications.

Urinary glycylprolyl dipeptidyl aminopeptidase (GP-DAP) in insulin-dependent diabetic patients

Urinary glycylprolyl dipeptidyl aminopeptidase (GP-DAP) concentrations were determined in 36 insulin-dependent diabetic children aged 4-18 years with a duration of diabetes ranging from 1 month to 14 years. Abnormal urinary GP-DAP concentrations were found in 19 of the 36 patients. Twelve of 27 patients without microalbuminuria also had increased urinary concentrations of GP-DAP. There was a significant correlation between urinary GP-DAP and plasma fructosamine (r = 0.52, p < 0.001). Our data suggest that urinary GP-DAP may be used as a marker for diabetic nephropathy. However, there is also a possibility that increased urinary GP-DAP concentrations are functionally related to poor metabolic control. Longitudinal studies are needed to establish the clinical usefulness of urinary GP-DAP.

Influence of carbohydrate moieties of human serum transferrin on the determination of its molecular mass by polyacrylamide gradient gel electrophoresis and staining with periodic acid-Schiff reagent

The influence of carbohydrate moieties of transferrin (Tf) on the determination of its molecular mass (MM) by polyacrylamide gradient gel electrophoresis (PAGGE) was investigated. Iron-free native human serum transferrin (Tf) of 99% purity and partly or completely carbohydrate- and N-acetylneuraminic acid (NANA)-free molecule forms were analyzed. The MM differences before and after enzymatic cleavage were found not to agree with the theoretical difference. From amino acid and carbohydrate analysis the MM of Tf was determined to be 79,570 Da whereas by denaturing and nondenaturing PAGGE MM of 77,000 Da +/- 1000 Da were found. After enzymatic cleavage of the two carbohydrate chains of Tf the difference between the calculated MM and the value reported in literature increased to 7000 Da (nondenaturing PAGGE) and 9200 Da (denaturing PAGGE). Following enzymatic cleavage of the 4 NANA molecules (MM 1237 Da) we obtained the relatively largest difference between the value given in the literature and that determined by PAGGE, namely MM 3300 Da on nondenaturing and 4000 Da on denaturing PAGGE. The differences due to the removal of the other carbohydrates were negligible. In addition we tested the periodic acid-Schiff reagent to stain iron-free Tf, containing different carbohydrate residues. The shortest carbohydrate moiety necessary for Tf staining corresponds to two identical carbohydrate chains of the structure (Asn)-GlcNAc-GlcNAc-beta-Man-(alpha-Man-)-alpha-Man.

Influence of isoproterenol-induced myocardial infarction on certain glycohydrolases and cathepsins in rats

The changes in the activities of certain lysosomal hydrolases, viz., beta-glucuronidase, beta-N-acetylglucosaminidase, beta-galactosidase, beta-glucosidase, alpha-glucosidase, alpha-galactosidase, alpha-mannosidase, cathepsin B, cathepsin D, and collagenolytic cathepsin, in serum and heart of rats subject to myocardial infarction with isoproterenol, were studied during the periods of peak infarction and recovery. The activities of all the enzymes assayed exhibited a significant increase both in serum and in heart at peak infarction stage and these levels returned to normal during the stage of recovery and repair. The infiltration of inflammatory cells at the infarct regions and the altered lysosomal fragility are probably responsible for the increased activity of the enzymes studied. This may also bring about the catabolism of connective tissue constituents as reported in literature.

Lysosomal enzyme levels in corneal storage media. K-Sol versus McCarey-Kaufman

Evidence indicates that lysosomal enzymes can carry out corneal autolysis during corneal storage and that they are damaging to the corneal endothelium. The authors investigated the release of lysosomal enzymes into two corneal storage media (K-Sol and McCarey-Kaufman [M-K]) by paired human donor corneas during 4 degrees C storage. The authors also studied the interaction of these media with lysosomal enzymes from human cornea. K-Sol and M-K stimulated (P less than 0.01) both beta-glucuronidase and alpha-galactosidase about equally. beta-N-Acetyl-glucosaminidase, a major catabolic enzyme of the cornea, was inhibited by the chondroitin sulfate in K-Sol by over 90% (P less than 0.01). Corneas stored in M-K released more lysosomal enzymes than corneas stored in K-Sol. At 4 days, the values approached significance (P less than 0.06) and by day 10 significantly higher values were found in the M-K media (P less than 0.01). Both storage methods showed a linear release. Individual corneas were found to vary in their release rates. Whether corneas that release more enzyme will show higher endothelial cell loss or produce less successful penetrating keratoplasty grafts deserves further study.

Catalytic activities of alkaline phosphatase and N-acetyl-beta-D-glucosaminidase in human cortical nephron segments: heterogeneous changes in acute renal failure and acute rejection following kidney allotransplantation

The catalytic activities of alkaline phosphatase and N-acetyl-beta-D-glucosaminidase, constituents of luminal brush-border membranes and lysosomes of kidney tubular cells, were measured in human kidney allografts in the maintenance and recovery phases of acute renal failure and in acute rejection crisis. The enzyme activities were fluorometrically determined in single microdissected cortical nephron segments of biopsies from 4 kidney allografts taken intraoperatively and postoperatively at different periods, which exhibited either good function or dysfunction. For comparison, the unaffected part of a human kidney nephrectomized due to hypernephroma as well as a biopsy of a morphologically normal human kidney were examined. Both enzymes displayed highest activities in the proximal part of the human nephron. In some intraoperative and postoperative biopsies with acute renal failure, alkaline phosphatase activity was reduced in proximal tubules, predominantly in the straight portion. This reduction could not be correlated with function. In acute rejection, very low alkaline phosphatase activities were uniformly found in proximal convoluted and straight tubules. Furthermore, intraoperative biopsies and biopsies of the functioning allograft have only approximately 50% of normal N-acetyl-beta-D-glucosaminidase activity in proximal convoluted tubules, but generally normal values in the straight portion. However, in acute renal failure, this enzyme activity was several-fold enhanced along the whole nephron, when compared with intraoperative values. In acute rejection, N-acetyl-beta-D-glucosaminidase activity was slightly reduced in proximal convoluted tubules, when compared with biopsies showing good function. It is suggested that the decrease of proximal tubular enzyme activities is the consequence of increased enzymuria and inadequate enzyme regeneration. On the other hand, the overshoot of N-acetyl-beta-D-glucosaminidase activity in the maintenance phase of acute renal failure appears to indicate increased degradative capacity, associated with cellular regeneration along the whole nephron.

Ocular neovascularization. Experimental animal model and studies on angiogenic factor(s)

We have been investigating experimentally the factors which initiate and perpetuate ocular neovascularization (NV). Our studies can be divided into four categories: production of a primate experimental model of ocular NV, morphological studies, tissue culture studies, and biochemical studies. We have been successful in producing a reliable primate model of ocular NV following retinal vein occlusion (RVO). The morphological and fluorescein angiographic studies have established that the new vessels seen in the animal model represent true NV and not simple dilatation of the pre-existing vessels. The tissue culture studies have shown the presence of vasoproliferative activity in the intraocular fluids in eyes with ocular NV in our animal model. The various biochemical studies conducted so far have provided preliminary results on various aspects, including the protein electrophoretic pattern and lysosomal enzymes in the intraocular fluids from eyes with and without ocular NV and effects of anoxia and of corticosteroids. The results of our various studies are very briefly reviewed and the importance of angiogenesis is discussed.

Beta-N-acetyl-glucosaminidase: possible role in ocular neovascularization

The possibility that lysosomal enzymes might be involved as angiogenic factors in ocular neovascularization (NV) was investigated. Beta-N-acetyl-glucosaminidase (NAGase) activity, and that of two other glycosidases, were present in the retinal derived protein fraction (RDPF) reported by others to be angiogenic. NAGase, but not the other glycosidases, was inhibited by vitreous. NAGase exhibited the same stability characteristics as RDPF. In diabetic rats there was a significant rise in vitreous but a fall in retinal NAGase activity. The sera of these animals, however, showed elevation in the activities of all five glycosidases. Preliminary experiments indicate that only the intermediate isoenzyme of NAGase, putatively insulin dependent, is elevated in the eyes of these diabetic rats. NAGase was also specifically elevated in the intraocular fluid from monkey eyes with retinal vein occlusion (RVO), and markedly so if NV was present. These results suggest the involvement of NAGase in the neovascular process in the eye.

Influence of streptozotocin- and alloxan-induced diabetes on the metabolism of glycosaminoglycans

GAG metabolism was investigated in rats with experimentally induced diabetes. In comparison to control animals, the uptake of 35S-sulfate was diminished in tissues of diabetic animals. Streptozotocin-induced diabetes showed a significant decrease in the content of GAG fractions except that of non-sulfated GAG in liver and kidney which was unchanged as compared to the control group. In rats rendered diabetic by alloxan, non-sulfated GAG increased appreciably in liver and kidney whereas highly sulfated GAG remained unchanged. In the skins of alloxan-diabetic rats both total and sulfated GAG decreased significantly. The activities of liver beta-glucuronidase, beta-N-acetyl glucosaminidase and cathepsin D were significantly increased in rats treated with streptozotocin and alloxan. In streptozotocin-diabetic rats, renal beta-glucuronidase and beta-N-acetyl glucosaminidase activities were reduced while cathepsin D activity was similar to that of controls. The renal beta-N-acetyl glucosaminidase and cathepsin D activities of alloxan-treated rats were not significantly different from normal but their beta-glucuronidase was significantly increased. In the spleen of streptozotocin-diabetic rats all the enzymes were increased except beta-N-acetyl glucosaminidase which remained unaltered. Increased excretion of uronic acid was observed in diabetic groups. These results collectively indicate that both streptozotocin- and alloxan-induced diabetes altered the synthesis and catabolism of GAG.

A beta-galactosidase isoenzyme from Turbo cornutus with substrate specificity toward GM1-ganglioside and glycoproteins

beta-Galactosidase from T. cornutus was resolved into two activity peaks by gel filtration column chromatography. The pH optima of the two peaks designated P1 and P2, were 5.5 and 3.0, respectively, when p-nitrophenyl-beta-D-galactopyranoside was used as the substrate. The molecular weights of P1 and P2 were 700,000 +/- 70,000 and 78,000 +/- 7800, respectively, when estimated by gel filtration chromatography. The activities of both forms of the enzymes are stimulated by anions such as Cl-, Br- and NO-3. While the activity of P1 was stimulated by low anion concentrations, P2 requires 700 times higher anion concentration for similar enhancement of activity. P1, the high molecular weight form hydrolyzes mainly galactose from small molecular weight beta-galactosides, such as p-nitrophenyl-beta-D-galactopyranoside, 4-methylumbelliferyl-beta-D-galactopyranoside, lactose, lactosylceramide and 3-O-beta-D-galactopyranosyl-D-arabinose, whereas P2, the low molecular weight form cleaves, in addition, all the beta-galactosides tested, including 2-hexadecanoylamino-4-nitrophenyl-beta-D-galactopyranoside, GM1-ganglioside, asialo-GM1-ganglioside, asialo fetuin, alpha 1-acid glycoproteins and the tryptic peptides of the glycoproteins. The optimal conditions for the hydrolysis of the terminal galactose from GM1-ganglioside which does not occur in gastropods, such as T. cornutus, was found to require 40 mM NaCl and 1 mM sodium taurodeoxycholate at pH 3.0 in 50 mM sodium citrate buffer, conditions similar to those by mammalian beta-galactosidase.

Isolation of autophagic vacuoles from rat liver: morphological and biochemical characterization

The induction of autophagy caused by vinblastine (VBL) has been found to be concomitant with a stimulation of proteolysis in a mitochondrial-lysosomal (ML) fraction from the rat liver (Marzella and Glaumann, 1980, Lab. Invest., 42: 8-17. Marzella and Glaumann, 1980, Lab. Invest., 42:18-27). In this fraction the enhanced proteolysis is associated with a threefold increase in the relative fractional volume of autophagic vacuoles (AVs). In an attempt to isolate the AVs, we subfractionated the ML suspension at different intervals after the induction of autophagy by VBL by centrifugation on a discontinuous Metrizamide gradient ranging from 50% to 15%. The material banding at the 24 to 20% and the 20 to 15% interphases was collected. Morphological analysis reveals that 3 h after induction of autophagy these fractions consist predominantly (approximately 90%) of intact autophagic vacuoles. These autophagic vacuoles contain cytosol, mitochondria, portions of endoplasmic reticulum, and occasional very low density lipoprotein, particles either free or in Golgi apparatus derivatives, in particular secretory granules. The sequestered materials show ultrastructural signs of ongoing degradation. In addition to containing typical autophagic vacuoles, the isolated fractions consist of lysosomes lacking morphologically recognizable cellular components. Contamination from nonlysosomal material is only a few percent as judged from morphometric analysis. Typical lysosomal "marker" enzymes are enriched 15-fold, whereas the proteolytic activity is enriched 10- to 20-fold in the isolated AV fraction as compared to the homogenate. Initially, the yield of nonlysosomal mitochondrial and microsomal enzyme activities increases in parallel with the induction of autophagy but, later on, decreases with advanced degradation of the sequestered cell organelles. Therefore, in the case of AVs the presence of nonlysosomal marker enzymes cannot be used for calculation of fraction purity, since newly sequestered organelles are enzymatically active. Isolated autophagic vacuoles show proteolytic activity when incubated in vitro. The comparatively high phospholipid/protein ratio (0.5) of the AV fraction suggests that phospholipids are degraded more slow than proteins. Is it concluded that AVs can be isolated into a pure fraction and are the subcellular site of enhanced protein degradation in the rat liver after induction of autophagy.

Plasma acidic glycohydrolases in insulin-dependent diabetes mellitus

We assayed plasma activities of beta-galactosidase, beta-hexosaminidase, alpha-fucosidase and alpha-galactosidase involved in degradation of the glycoprotein molecule in 110 insulin-dependent diabetics aged 3-1/2 to 19 years and compared them to a group of normal youngsters. We correlated the plasma enzyme activities with the duration, control and sequelae of insulin-dependent diabetes. Insulin-dependent diabetics had a significantly higher plasma activity of beta-hexosaminidase and alpha-mannosidase (p less than 0.01) and a significantly lower plasma activity of alpha-fucosidase and alpha-galactosidase (p less than 0.01). Of the 5 enzymes studied, only plasma beta-hexosaminidase correlated with fasting and postprandial blood sugar (p less than 0.01), cholesterol and triglycerides (p less than 0.05). Additionally, poor control of diabetes was also associated with a significantly higher plasma beta-hexosaminidase activity (p less than 0.01). Proteinuria or an abnormal Addis count suggestive of renal involvement was associated with various changes in plasma acidic hydrolases. These changes may be related to insulin deficiency rather than hyperglycemia and may be genetically determined.

The effects of parabiosis on serum and kidney glycosidase activities in spontaneously diabetic mice

Spontaneously diabetic non-obese mice of the ICR strain were newly inbred in Shionogi laboratory, Japan. Animals became diabetic suddenly, more frequently and severely in females. Blood glucose levels were 452 +/- 73 mg/100 ml with serum insulin levels of less than 1.0 microU/ml in the fed state. Parabiosis with normal control ICR mice for 2 weeks decreased the blood glucose level to 260 +/- 51 mg/100 ml (P less than 0.01) and resulted in serum insulin levels of 46.0 +/- 18.0 microU/ml (P less than 0.01). Kidney homogenate beta-N-acetylglucosaminidase and beta-galactosidase activities were reduced in diabetic mice (42% and 44% decreases respectively) (P less than 0.025 and P less than 0.001), and restored almost to normal after 2 weeks of parabiosis. Renal alpha-mannosidase activity was decreased 43% (P less than 0.001) in the diabetic mice but unaffected by parabiosis. Serum beta-N-acetylglucosaminidase, beta-galactosidase and alpha-glucosidase activities were significantly increased in diabetic mice (179%; 233% and 58% increase respectively) (P less than 0.005, P less than 0.001 and P less than 0.001), and returned to normal with parabiosis.

Quantitative distribution of lysosomal hydrolases in the rat nephron

The activities of N-acetyl-beta, D-glucosaminidase (NAG, EC 3.2.1.30), beta, D-galactosidase (beta-gal, EC 3.2.1.23) and acid phosphatase (ac-Pase, EC 3.1.3.2) were measured in the glomeruli, five segments of the proximal and four segments of the distal tubule of normal male Wistar rats. The activities of NAG and beta-gal are 3- to 5-fold higher in the first part of the proximal tubule than in other segments and very low in glomeruli. We propose that the distribution of these two glycosidases reflects the contribution of the different tubular segments to the reabsorption of glycoproteins. The maximal activity of ac-Pase was found in the straight part of the proximal tubule. It was only 1.5-fold higher than in the distal tubule. Moreover, the activity in glomeruli is rather high. We conclude that ac-Pase is not primarily involved in the handling of reabsorbed molecules.

Recognition of self and nonself, the crucial role of phagocytosis and lysosomal destruction of antigen

Primitive animals possess the ability to take up foreign matter and degrade it intracellularly. It is unlikely that during the evolution of the immune apparatus this mode of dealing with the foreign material would be bypassed. It is suggested that phagocytosis and intracellular digestion of the antigen is the primary mode of defense, and that failing complete digestion of the antigen an antibody response occurs. Phagocytosis of the antigen is known to be a necessary step in the process of antibody formation. Following the uptake by macrophages, the antigen is concentrated within the lysosome and subjected to the action of hydrolytic enzymes. Lysosomes are also the sites of catabolism of body constituents, and are believed to contain enzymes necessary for complete digestion of self constituents. If the lysosomal enzymes can completely degrade the antigen, the latter's possible harmful effects would be destroyed. The organism then does not need to waste energy in the synthesis of specific antibody, the function of which now is redundant. If the lysosomal enzymes cannot hydrolyze the antigen completely, the hydrolysis-resistant fragment can be transferred to lymphocytes, where it can induce antibody synthesis. Thus, the ability of the host hydrolytic enzymes to degrade a substance completely constitutes the recognition of self and the inability to do so amounts to the recognition of nonself.

Leucocyte migration and lysosomal enzymes release in rat carrageenin pleurisy

The time course of rat carrageenin pleurisy has been studied. The inflammatory reaction is characterized by exudate formation and massive leucocyte emigration into the pleural space both reaching peak values at 24 hours. Moreover betaglucuronidase, acid phosphatase and lactic dehydrogenase have been assayed in the exudate. The activity of lysosomal enzymes parallels the severity of the inflammatory response, while that of cytoplasmic enzyme lactic dehydrogenase resulted unmodified. Treatment of animals with indomethacin, phenylbutazone, aspirin and flufenamic acid inhibited both exudate formation and leucocyte emigration. In contrast none of these drugs was able to reduce lysosomal enzyme release.

Isoelectric-focusing behavior of acid hydrolases in rat kidney lysosomes. Effects of the pH gradient, autolysis and neuraminidase

Isoelectric focusing was used to study the multiple forms of acid phosphatase, arylsulfatase, beta-glucuronidase and beta-N-acetylhexosaminidase in lysosomes isolated from rat kidney. The isoelectric points of the main protein and hydrolase peaks were 1-1.5 units lower when electrofocusing was done in a pH 3-10 gradient than in a pH 10-3 gradient, apparently because the lysosomal constituents aggregated strongly at their isoelectric points and tended to settle somewhat in the gradient due to gravity. In the extended pH gradient the acidic form of each hydrolase occurred as asingle, relatively discrete peak. However, when pooled acidic fractions were refocused in a restricted pH gradient (pH 6-3 or 3-5) multiple acidic enzyme and protein components were resolved with isoelectric points between 2.7 and 5.1. When autolysis was minimized by extracting lysosomal fractions at alkaline pH (0.2% Triton X-100, 0.1%p-nitrophenyloxamic acid, 0.1 M glycine buffer, pH9) and including 0.1%p-NITROPHENYLOXAMIC ACID, AN INHIBITOR OF LYSOSOMAL NEURAMINIDASE AND CATHEPSIN D, in the pH gradient, arylsulfatase, beta-glucuronidase and beta-N-acetylhexosaminidase occurred in two forms, an acidic form with an isoelectric point of about 4.4, and a basic form with an isoelectric point close to 6.2, 6.7 and 8.0, respectively. Acid phosphatase occurred in three forms with isoelectric points of 4.1, 5.6 and 7.4. When some autolytic digestion was permitted by extracting lysosomal fractions in an acidic medium (0.2% Triton X-100, 0.1 M sodium acetate buffer, pH 5.2) AT 0-4DEGREES C and omitting p-nitrophenyloxamic acid from the gradient, the acidic form of beta-glucuronidase and the intermediate form of acid phosphatase were lost, the isoelectric points of the acidic forms of acid phosphatase, arylsulfatase and beta-N-acetylhexosaminidase were increased 0.6-1.2 units, and the isoelectric point of the basic forms of acid phosphatase, arylsulfatase and beta-glucuronidase was increased 0.5 unit. When lysosomal extracts were incubated with bacterial neuraminidase before electrofocusing, the acidic forms of acid phosphatase, arylsulfatase and beta-glucuronidase were largely lost, the isoelectric point of the acidic form of beta-N-acetylhexosaminidase was increased from 4.5 to 6.4, and the isoelectric points of the basic forms of all four hydrolases were increased 0.5-1.5 units. Autoincubation of lysosomal extracts in vitro at pH 5.2 PRODUCED SIMILAR, THOUGH LESS MARKED, effects. cont'd

Autolysis of glycoproteins in rat kidney lysosomes in vitro. Effects on the isoelectric focusing behaviour of glycoproteins, arylsulphatase and beta-glucuronidase

1. Rat kidney lysosomal glycoproteins, prelabelled in the N-acetylneuraminic acid and polypeptide portions with N-acetyl[(3)H]mannosamine and [(14)C]lysine, or with N-acetyl-[(14)C]glucosamine, were incubated under various conditions. Autolytic cleavage of labelled N-acetylneuraminic acid and peptide was maximum at pH5.0. 2. N-Acetylneuraminic acid was released more rapidly than peptide during incubation at 37 degrees or 4 degrees C at pH5. p-Nitrophenyloxamic acid, an inhibitor of bacterial neuraminidase (Edmond et al., 1966), inhibited the cleavage of N-acetylneuraminic acid and peptide, and also inhibited cathepsin D activity. 3. Galactono-, mannono-, and glucono-lactone, inhibitors of the corresponding glycosidases, blocked the autolytic cleavage of N-acetyl[(14)C]glucosamine and protein without inhibiting beta-N-acetylhexosaminidase or cathepsin D activity. These findings suggest that the carbohydrate side chains protect the polypeptide portion of the lysosomal glycoproteins against proteolytic attack by lysosomal cathepsins. 4. In electrofocusing experiments, autolysis was minimized by adding 0.1% p-nitrophenyloxamic acid to the media used for extraction and electrofocusing, and by maintaining an alkaline pH (pH8.8-9) during extraction and dialysis. Arylsulphatase occurred in two forms with pI values of 4.4 and 6.4-6.7, and beta-glucuronidase in two forms with pI values of 4.4 and 6.1. When [(14)C]lysine and N-acetyl[(3)H]mannosamine were given to rats 1.5 and 1 h before killing, (14)C and (3)H were largely restricted to highly acidic glycoprotein species with pI values of 2.1-5.1. 5. When a lysosomal extract was adjusted to pH5 and incubated at 20 degrees C for 16h and then at 37 degrees C for 1 h before electrofocusing, 32 and 58% of the labelled peptide and N-acetylneuraminic acid was cleaved and the pI values of the labelled glycoproteins were markedly increased. About 80% of the acidic form of arylsulphatase and beta-glucuronidase was recovered with the basic form, and the pI of the basic form of both enzymes rose to 7.0. Similar, though less marked changes, were observed when a lysosomal extract was kept at pH5 for 2h at 4 degrees C before electrofocusing. 6. When an acidic lysosomal fraction (pI4.2-4.6) was incubated at pH5 for 2.5h and refocused, 80% of the arylsulphatase now occurred in two forms with pI values of 5 and 6.4. When a basic lysosomal fraction (pI5.8-6.4) was similarly incubated, the pI of arylsulphatase increased from 6.4 to 7.2. The relative increase in pI of arylsulphatases was accompanied by a proportional loss of N-acetylneuraminic acid from the glycoprotein associated with these forms. 7. These experiments show that lysosomal glycoproteins and two representative hydrolases, when exposed to a mildly acidic pH, readily undergo autolytic degradation and their pI values increase. These observations may have a bearing on the origin of the molecular heterogeneity of the lysosomal enzymes.

Hydrolysis of GM1-ganglioside by human liver beta-galactosidase isoenzymes

1. GM(1)-ganglioside, specifically tritiated in the terminal galactose, was hydrolysed by two forms of ;acid' methylumbelliferyl beta-galactosidase isolated on gel filtration. 2. Identification of GM(1)-ganglioside beta-galactosidase activity with the ;acid' methyl-umbelliferyl beta-galactosidases was based on the following: coincident elution profiles on gel filtration; simultaneous inactivation by heat and other treatments; stabilization of both activities by chloride ions; mutual inhibition of hydrolysis by the two substrates. 3. The two isoenzymes (I) and (II) showed general requirements for a mixture of anionic and nonionic detergents in the hydrolysis of the natural substrate. 4. Isoenzyme (I) differed from (II) in molecular size, pH-activity profile, relative resistance to dilution and in sensitivity to various inhibitors. 5. The most significant difference between the isoenzymes is in substrate saturation kinetics: (I) was hyperbolic whereas (II) was sigmoid. The apparent Michaelis constants were 28mum for (I) and 77mum for (II). Isoenzyme (I) was insensitive to GM(2)-ganglioside whereas (II) was inhibited, consistent with the hypothesis that GM(1)-ganglioside (and its analogue) acts as modifier in isoenzyme (II) but not in (I). 6. Isoenzyme (I) was membrane-bound whereas (II) was soluble; the former probably represents isoenzyme (II) bound to membrane components, thereby becoming activated. 7. Membranes may serve a dual role in enzyme catalysis involving lipids: as a medium where both enzyme and substrate are effectively concentrated, and as actual activator of enzymes through binding of the latter to specific membrane components.