Studies of the acetyl-CoA-binding site of rat liver spermidine/spermine N1-acetyltransferase

Rat liver spermidine/spermine N1-acetyltransferase was found to be strongly inhibited by the dyes Cibacron F3GA, Coomassie Brilliant Blue and Congo Red. Inhibition was competitive with respect to acetyl-CoA and Ki values of 0.7 microM and 52 microM were determined for Cibacron F3GA and Coomassie Brilliant Blue respectively. The enzyme was strongly retained by columns of Affi-Gel Blue, which contains Cibacron F3GA linked to agarose. It was not eluted from this adsorbent in the presence of 10 mM-spermidine/0.5 M-NaCl/50 mM-Tris/HCl, pH 7.5, but was released by 1 mM-CoA in 10 mM-spermidine/50 mM-Tris/HCl, pH 7.5. These results are consistent with the presence in the enzyme of a dinucleotide fold that binds acetyl CoA and has a high affinity for Cibacron F3GA. The spermidine/spermine N1-acetyltransferase was irreversibly inactivated by exposure to butane-2,3-dione in sodium borate, pH 7.8, or by exposure to phenylglyoxal or camphorquinone-10-sulphonic acid. All of these reagents are known to interact with arginine residues in proteins under the conditions in which they inactivated the acetyltransferase. Inactivation was prevented by the presence of acetyl-CoA or CoA, but to a lesser extent by 3'-dephospho-CoA and not at all by NAD or adenosine. This protection suggests that an arginine residue at the active site is involved in the binding of the acetyl-CoA substrate. Treatment of the assay mixture but not the spermidine N1-acetyltransferase with alkaline phosphatase prevented the reaction taking place. This suggests that the apparent loss of enzyme activity in response to alkaline phosphatase reported by Matsui, Otani, Kamei & Morisawa [(1982) FEBS Lett. 150, 211-213] is due to dephosphorylation of the acetyl-CoA substrate and that the 3'-phosphate group is essential for activity.

Influence of taurocholate on hepatic clearance and biliary excretion of asialo intestinal alkaline phosphatase in the rat in vivo and in isolated perfused rat liver

We have used canine intestinal alkaline phosphatase, an asialoglycoprotein, as a tool to study the effect of taurocholate on hepatic asialoglycoprotein transport. After bolus injections of 20 U of alkaline phosphatase into anesthetized rats in vivo and isolated perfused rat livers, a biexponential disappearance pattern was observed; 6.2% of the dose and 0.8% of the dose was excreted in bile, respectively. Taurocholate infusion in vivo and in isolated perfused livers resulted in a virtually complete abolition of the plasma disappearance of alkaline phosphatase in the second slow phase of the curve, whereas the primary disappearance rate was not affected. Wash out experiments showed release of exogenous alkaline phosphatase from the liver, which was strongly increased by taurocholate. Liver perfusion experiments with two subsequent doses of alkaline phosphatase indicated that the taurocholate effect was completely reversible. It is concluded that taurocholate enhances exocytosis of interiorized alkaline phosphatase from liver into plasma. The taurocholate effect on hepatic exocytosis of the asialoglycoprotein may also occur when bile salt concentrations in the systemic or portal circulation, or both, are elevated due to certain liver diseases and postprandial bile salt absorption.

Alteration of adenylate cyclase activity by phosphorylation and dephosphorylation

Incubation of S49 cell membranes at 0 degree C resulted in a loss of adenylate cyclase activity, but addition of ATP and ATP regenerating system prevented the decrease of the activity. A non-phosphorylating analogue of ATP, adenyl-5'-yl imidodiphosphate, was less effective than ATP. Treatment of solubilized adenylate cyclase with calf intestine alkaline phosphatase caused the decrease of the activity. Membranes from cyc- S49 mutant cells, which are devoid of guanine nucleotide-binding protein, yielded the same results as membranes from S49 cells, indicating that the catalytic component is involved in the alteration of the enzyme activity by these treatments. These results suggest that phosphorylation and dephosphorylation of the catalytic component may regulate adenylate cyclase activity.

Enzymatic transfer of galactosyl phosphate from UDP-galactose to UDP-N-acetylglucosamine

The microsomal fraction of hen oviduct homogenate has been shown to contain an enzyme capable of catalyzing a transfer of galactosyl phosphate from UDP-galactose to UDP-N-acetylglucosamine. The product was isolated and identified as UDP-N-acetylglucosamine-6-phosphogalactose, the same compound as that found as a normal constituent in hen oviduct. The enzyme is analogous in reaction type to UDP-N-acetylglucosamine: glycoprotein N-acetylglucosamine-1-phosphotransferase (the enzyme responsible for introducing the recognition marker of newly synthesized lysosomal enzymes), which suggests that the galactosyl phosphotransferase is involved in galactose 1-phosphate transfer to N-acetylglucosamine residues of newly synthesized glycoproteins.

Phosphorylation of cytochrome-P-450-dependent monooxygenase components

Most chemical carcinogens require activation by polysubstrate monooxygenase. The phosphorylation of essential components of this cytochrome P-450 monooxygenase system, isolated from rabbit liver microsomes, cytochrome P-450 (LM2) and cytochrome reductase, was tested using two different protein kinases. One of the kinases, a cyclic AMP-independent phosvitin kinase (kinase P), was inactive in all systems tested. However, the catalytic subunit of a cyclic AMP-dependent protein kinase (kinase C) catalyzed phosphoryl group transfer to both proteins, but to different extents. Cytochrome P-450 was phosphorylated when added as sole component and also when in the presence of P-450 reductase and phosphatidylcholine. In contrast, the weak phosphorylation of P-450 reductase was reduced considerably in a complete reconstituted system containing P-450 and phosphatidylcholine. The inclusion of kinase P did not alter these results which excludes the possibility that these kinases participate in a sequential phosphorylation mechanism. The monooxygenase constituents themselves were without kinase activity. When hepatic microsomes were isolated in presence of the phosphatase inhibitor sodium fluoride no significant change in monooxygenase (7-ethoxycoumarin O-deethylation) activity was observed, whilst after preincubation with either acid or alkaline phosphatase a significant reduction in monooxygenase activity was measured. Thus, cytochrome P-450 (LM2) is phosphorylatable by protein kinase C and the catalytic activity of polysubstrate monooxygenase decreases after preincubation of microsomes with phosphatases.

Application of the nitrocellulose transfer technique and alkaline phosphatase conjugated anti-immunoglobulin for determination of the specificity of monoclonal antibodies to protein mixtures

The target antigens of a series of monoclonal antibodies raised against a complex mixture of proteins have been identified. The protein mixture was fractionated by polyacrylamide gel electrophoresis in SDS, and the fractionated proteins electrophoretically transferred to nitrocellulose sheets. Protein bands reacting with antibody were identified by incubating the nitrocellulose strips with the 'hybridoma' culture supernatants, followed by detection of bound antibody using alkaline phosphatase conjugated to rabbit anti-mouse F(ab')2 antibody, and histochemical substrates. With this technique, the antigens reacting with 4 of a series of 5 monoclonal antibodies have been identified.

Site-specific phosphorylation regulates the transcriptive activity of vesicular stomatitis virus NS protein

In vitro transcription by vesicular stomatitis virus nucleocapsids is inhibited by enzymatic dephosphorylation of the NS protein. We provide evidence that specific, partial dephosphorylation of NS molecules is the only detectable change in nucleocapsids treated with bacterial alkaline phosphatase under conditions that prevent the action of adventitious protease. Dephosphorylation appeared to affect only the rate of transcription; there were no changes in sedimentation rates of transcripts. To identify the sites of phosphorylation required for NS activity in transcription, we examined phosphopeptides produced by chymotrypsin digestion of the two electrophoretic classes of NS molecules found in virions and infected cells. The electrophoretically slower class, NS1, abundant in the intracellular soluble pool, has a lower activity in transcription; it contained six chymotryptic phosphopeptides. Five of these peptides contained both phosphoserine and phosphothreonine, indicating that this peptide cluster represents at least 11 separate sites of phosphorylation. In the electrophoretically faster nucleocapsid-associated NS2 class of molecules, which support a higher rate of transcription, another group of eight phosphopeptides was superimposed on this pattern. Two of these peptides contained both phosphoserine and phosphothreonine, so this cluster of peptides represents at least 10 additional phosphorylation sites. These sites were especially sensitive to dephosphorylation by bacterial alkaline phosphatase. One or more of them appears to be responsible for the higher transcription rates medicated by NS2 molecules.

Specificity and localization of the hepatitis B virus-associated protein kinase

The nature of the protein kinase (PK) which phosphorylates the core protein of hepatitis B virus in vitro was studied. The PK copurified with the core particles during rate zonal centrifugation and gel chromatography. It showed the same size heterogeneity as the core particles, which consisted of a main fraction of 28-nm particles and a subfraction of 22- to 26-nm particles. DNA-containing heavy core particles with a density of 1.33 to 1.35 g/ml and less endogenous PK than did the light cores. The phosphorylation reaction had a rapid initial phase (several minutes) and a slow but long-lasting second phase (many hours). The PK had a high affinity for ATP (KM = 0.5 mumol/liter). Only few of the several hundred P21.9 subunits in one core particle were phosphorylated in vitro. The only amino acid which was phosphorylated in vitro was serine. The resistance of the introduced phospho group against alkaline phosphatase showed that the PK acceptor, and probably the enzyme itself, was located inside the core particle.

Rat liver cholesterol 7 alpha-hydroxylase. Modulation of enzyme activity by changes in phosphorylation state

Four lines of evidence presented here suggest that the activity of cholesterol 7 alpha-hydroxylase in rat liver is modulated by changes in its phosphorylation state. 1) Livers were homogenized and microsomes were isolated and washed in the presence of either 50 mM NaCl or 50 mM NaF, the latter an inhibitor of phosphoprotein phosphatases. The 7 alpha-hydroxylase activity of microsomes prepared with NaF was 80% greater than that of microsomes prepared with NaCl. 2) Incubation of 10,000 X g supernatants from rat liver for 20 min at 37 degrees C in the absence of 50 mM KF decreased the activity of microsomal cholesterol 7 alpha-hydroxylase by 52%. No significant change was seen in the presence of KF. 3) 7 alpha-Hydroxylase activity fell by 40% when microsomes were incubated with bacterial alkaline phosphatase compared to incubation of microsomes with phosphatase that was inhibited by phosphate and EDTA. 4) 7 alpha-Hydroxylase activity increased by 22% when phosphatase-treated microsomes were incubated for 40 min at 37 degrees C with 1 mM MgATP, 50 microM cAMP, and 200 units of cAMP-dependent protein kinase.

Nuclear ligation of RNA 5'-OH kinase products in tRNA

Mouse L-cell nuclei incorporate gamma-32P from ATP in vitro predominantly in 5'-monophosphoryl termini and internal phosphodiester bonds with a nonrandom nearest-neighbor distribution. In the presence of 1 microgram of alpha-amanitin per ml the gamma-32P showed a time-dependent appearance in RNA bands which migrated with mature tRNA species but not with pre-tRNA and 5S RNA. The gamma-32P was found in internal phosphodiester bonds as shown by alkaline phosphatase resistance and was identified in 3'-monophosphates after RNase T2, T1, and A digestion. The specificity of this incorporation was indicated by a limited number of labeled oligonucleotides from a T1 digest and identification of 70 to 80% of the 32P label as Cp on complete digestion of the eluted tRNA band. We also observed transiently [gamma-32P]ATP-labeled RNA bands (in 5'-monophosphate positions) that were 32 to 45 nucleotides long. The results presented suggest splicing of several mouse L-cell tRNA species in isolated nuclei which involve the RNA 5'-OH kinase products as intermediates.

How complement kills E. coli. I. Location of the lethal lesion

We have studied the action of human complement (C) on E. coli membranes. We find, as have others, that C disrupts the outer membrane (OM), allowing the release of periplasmic proteins. In addition, we have found 1) that in the complete absence of lysozyme, C damages the inner membrane (IM), 2) IM damage is different from OM damage in that only small molecules traverse a damaged IM whereas macromolecules traverse damaged OM, 3) IM damage and OM damage occur with identical kinetics and dose response, suggesting that IM and OM damage are closely coupled events, and 4) upon the addition of purified C8 and C9 to the washed cellular intermediate, E. coli C 1-7, both IM and OM are damaged coordinately. These results, taken together, suggest that C damages E. coli membranes by acting at a site contiguous with both membranes. We speculate that C may simultaneously gain access to both membranes by acting at the junctions between IM and OM.

Analysis of the biosynthesis of HLA-DR glycoproteins in human malignant melanoma cell lines

Human malignant melanoma cell line SK-MEL-37 expresses HLA-DR antigens having a characteristic 2-chain structure, with heavy chains (alpha) of approximately 32,000 daltons and light chains (beta) of approximately 28,000 daltons. Nonequilibrium pH-gradient electrophoresis (NEPHGE) on HLA-DR immunoprecipitated by rabbit anti-HLA-DR sera from [35S]-methionine-labeled, pulse-chased cells showed 2 closely spaced heavy-chain components (1, 2) and 4 light-chain spots (3-6). From nonchased samples, numerous more-basic components running in the heavy chain region were also precipitated. In particular, a very basic, 30,000 dalton component (pl approximately 8.5) was prominent (component 7); this spot probably corresponds to the invariant (Ii) peptide previously demonstrated in lymphoid cell HLA-DR precipitates (9) and the M-1 peptide of Shackelford and Strominger (10). None of these components (alpha, beta, or component 7) was precipitated from extracts of HLA-DR-negative melanoma cells. Pulse-chase experiments and the use of different labeled sugar precursors showed that component 7 is a partially glycosylated intracellular precursor, possibly of the HLA-DR alpha-chain. None of the immunoprecipitates, even from cells pulse-labeled for only 15 min, contained a peptide migrating in the 55,000 to 60,000 m.w. region. It was concluded that melanoma HLA-DR is not synthesized via a polyprotein precursor. In contrast to these results, obtained with rabbit anti-HLA-DR sera, a mouse monoclonal anti-HLA-DR was found to precipitate only biosynthetically completed alpha (1, 2) and beta (3-6) chains.

Binding of fibronectin to Clq; inhibition of binding by aggregated IgG

Fibronectin was shown to bind to C1q using alkaline phosphatase conjugated fibronectin and C1q coated polystyrene tubes. The binding of the alkaline phosphatase conjugated fibronectin to C1q was dose dependent and inhibited by fibronectin and by the sulfated polymers heparin and chondroitin sulfate. The fibronectin interaction was inhibited only slightly by gelatin indicating that the fibronectin-gelatin interaction was different from that with C1q. Heat aggregated IgG blocked the binding of fibronectin to C1q and fibronectin inhibited the binding of aggregated IgG to C1q. These results suggest that fibronectin may be a factor affecting the determination of immune complexes in serum specimens by C1q binding assays.

[Recovery of the sensitivity of J-41 cells to Coxsackie B3 virus by treatment with exogenous alkaline phosphatase]

It has been shown that injection of G-41 cell cultures, deficient as regards alkaline phosphatase and resistant to Coxsackie B3 virus, in conjunction with exposure to an alkaline phosphatase preparation from the calf intestine results in virus reproduction. Depending on the dose administered and multiplicity of infection there occur either complete destruction of the monolayer or death of some cells with the development of cytopathic changes specific for Coxackie virus.

Effects of vasodilator drugs, alkaline phosphatase, and cyclic AMP-dependent protein kinase on the 45calcium uptake of sarcolemmal microsomes from human umbilical arteries

1 A microsomal fraction was prepared from human umbilical arteries by differential centrifugation. The preparation was capable of an oxalate-stimulated Ca2+ uptake at a mean rate of 0.74 nmol Ca2+ mg-1 protein min-1 which could be inhibited by a Ca2+ ionophore, A 23 187, and by Tween 80. 2 The rate of Ca2+ uptake in the fraction obtained by density gradient fractionation paralleled 5'-nucleotidase activity suggesting that vesicles of predominantly sarcolemmal origin were responsible for the microsomal Ca2+ uptake. 3 Cyclic adenosine 3',5'-monophosphate-dependent protein kinase enhanced membrane phosphorylation but did not affect Ca2+ uptake. Preincubation with alkaline phosphatase reduced membrane phosphorylation to a greater extent than Ca2+ uptake. These data are not in favour of a close correlation between Ca2+ uptake and phosphorylation. 4 None of 15 vasodilator drugs (bencyclane, carbocromen, diazoxide, dilazep, hydralazine, indapamide, isosorbide dinitrate, methyl-isobutyl-xanthine, minoxidil, naftidrofuryl, nitroglycerine, prenylamine, sodium nitroprusside, tetracaine, and verapamil) had any effect on Ca2+ uptake at 10(-5) M. This suggests that vasodilator drugs do not act by a direct influence on the Ca2+ pumps of vascular smooth muscle cells.

Feedback regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase in livers of mice treated with mevinolin, a competitive inhibitor of the reductase

Compactin (ML-236B) and the related compound, mevinolin, are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase), the rate-controlling enzyme in cholesterol synthesis. Previous studies have shown that administration of compactin to cultured cells elicits a compensatory increase in the amount of HMG CoA reductase in the cells. A similar increase in HMG CoA reductase has been reported in livers of rats and mice that have been treated with compactin. In this study, we explore the mechanism for the mevinolin-mediated increase in hepatic HMG CoA reductase in mice that have been fed a control diet and a 2% cholesterol diet. Administration of mevinolin to mice on a control diet produced a 6- to 10-fold increase in the amount of HMG CoA reductase in liver microsomes. When mice were fed the cholesterol-enriched diet, cholesterol accumulated in the liver and HMG CoA reductase declined by 90%. The administration of mevinolin to cholesterol-fed mice produced a three to eightfold increase in HMG CoA reductase. Despite the abundant amount of cholesterol that was already present in the livers of the mevinolin-treated, cholesterol-fed animals, their elevated HMG CoA reductase could be rapidly suppressed by the subcutaneous injection of small amounts of mevalonate, the product of HMG CoA reductase. These data are compatible with the existence in mouse liver of a multivalent feedback regulatory mechanism for HMG CoA reductase in which suppression of the enzyme requires both a sterol and a nonsterol substance derived from mevalonate. By blocking mevalonate synthesis, mevinolin activates this regulatory mechanism, and this in turn causes an increase in hepatic HMG CoA reductase. The ability to suppress the elevated HMG CoA reductase with mevalonate may prove useful in potentiating the effectiveness of mevinolin as a hypocholesterolemic agent.

Resistance to the antibiotics viomycin and capreomycin in the Streptomyces species which produce them

Viomycin capreomycin, antibiotics produced by Streptomyces vinaceus and S. capreolus respectively, are potent inhibitors of bacterial protein synthesis. Although these organisms are highly tolerant of their own products in vivo, their ribosomes are fully sensitive to the action of the drugs in vitro. However, they processes novel, antibiotic-inactivating enzymes (viomycin phosphotransferase, capreomycin phosphotransferase, capreomycin acetyltransferase) which, in addition to possible biosynthetic roles, may contribute to the resistances observed in vivo.

Soluble arylsulfatases of human brain and some characteristics of the brain-specific arylsulfatase Bm

The brain-specific arylsulfatase Bm (aryl-sulfate sulfohydrolase, EC 3.1.6.1) was demonstrable in human and monkey brain. Arylsulfatases A, B and Bm were separated employing DEAE-cellulose chromatography. There was a distinct difference in the proportion of the sulfatases in infant and adult human brain. Arylsulfatase Bm after concanavalin A-Sepharose chromatography showed the property of binding to Sephadex G-200 totally. Several dissociating agents failed to elute the enzyme from the bound form. Under similar conditions arylsulfatase A did not show any binding to Sephadex. On treatment with Escherichia coli alkaline phosphatase adult human brain arylsulfatase Bm but not arylsulfatase A was converted into a less acidic, presumably dephosphorylated form that did not bind to DEAE-cellulose. Monkey brain arylsulfatase Bm showed a similar susceptibility to E. coli phosphatase treatment. Inorganic phosphate and serine phosphate but not mannose 6-phosphate could inhibit this dephosphorylation. There were differences in the susceptibilities to alkaline phosphatase treatment of the arylsulfatase Bm from infant and adult human brain. Endogenous phosphatase also seemed to have a role on the phosphorylated state of arylsulfatase Bm.

Properties of a factor in cytosol that enhances hormones-stimulated adenylate cyclase activity

1. The addition of 50 000g cytosol preparations of isolated human platelets, cultured rat osteogenic sarcoma or cultured bone cells to particulate preparations of adenylate cyclase, from the same or unrelated tissues, caused marked enhancement of the hormone-stimulated enzyme activities. 2. The degree of enhancement obtained by addition of the cytosol preparations was similar to that observed on addition of GTP. 3. The enhancing activity of the three cytosol types was found to be sensitive to digestion by trypsin and alkaline phosphatase, partially heat-labile and partially inactivated by exposure to charcoal. 4. Gel filtration studies indicated an apparent molecular weight of 20 000--30 000. Further, the 20000-30000-mol.wt. fractions obtained by gel filtration could enhance the adenylate cyclase activity of particulate preparations derived from unrelated cell types. 5. The results suggest a common or similar adenylate-cyclase-enhancing factor or factors, protein in nature, present in the three cytosol types.

Chick embryo fibroblasts produce two forms of hyaluronidase

Cultured chick embryo fibroblasts derived from skin and skeletal muscle exhibit hyaluronidase activity both associated with the cell layer and secreted into the medium. Although both forms of the enzyme have a number of similar characteristics (R.W. Orkin and B.P. Toole, 1980, J. Biol. CHem. 255), they differ in thermal stability at neutral pH and in behavior on ion-exchange chromatography. Both forms of the enzyme are equally stable at acidic pH for long intervals, but the cell-associated hyaluronidase is significantly less stable than the secreted froms at neutral pH and at temperatures more than or equal to 30 degrees C. Neither the presence of proteases nor inhibitors of hyaluronidase appear to be involved in the cell-asspcoated enzyme. Chromatography of the two forms of hyaluronidase on carboxymethyl cellulose reveals that most (60-90 percent) of the secreted form of the enzyme elutes at a lower ionic strength than the cell- associated enzyme. Treatment of the secreted form of hyaluronidase with neuraminidase shifts its elution profile on carboxymethyl cellulose toward that of the cell-associated form, and also decreases its thermal stability at neutral pH. In contrast, treatment of the secreted form of hyaluronidase with alkaline phosphatase has no detectable effect. These data suggest that the secreted hyaluronidase differs from the cellular form in possessing additional sialic acid residues which endow the former with increased stability in the extracellular milieu.

Inhibitors of platelet aggregation in the fetoplacental unit and myometrium with particular reference to the ADP-degrading property of placenta

Extracts of fresh tissue from the feto-placental unit and myometrium were tested for their ability to inhibit ADP-induced platelet aggregation and to degrade ADP. Placental extracts caused rapid reversal of aggregation and degraded ADP, both effects being mimicked by HPAP. However, whereas the latter was inhibited by L-phenylalanine but not by heating to 65 degrees C for 5 minutes, the reverse was true for crude placental extracts. Umbilical cord vessels and myometrium totally inhibited platelet aggregation in a similar way to pure PGI2. Both tissues also exhibited ADP-ase activity but were much less potent in this respect than placenta. In the system used, little or no anti-aggregatory activity was detected in extracts of non-vascular cord tissue, fetal membranes or amniotic fluid, although the two latter tissues had a weak ADP-degrading effect. Thus, it appears that in contrast to myometrium and umbilical cord vessels, the major inhibitor of platelet aggregation in placenta is an ADP-ase and not PGI2. While part of the inhibitory effect of placenta may be due to HPAP, other ADP-degrading enzymes also seem to contribute to the overall anti-aggregatory property of this organ.

Fibroblast receptor for lysosomal enzymes mediates pinocytosis of multivalent phosphomannan fragment

Mild acid hydrolysis of phosphomannan secreted by the yeast hansenula holstii (NRRL Y- 2448) produces two phosphomannyl fragments which differ strikingly in their potency as inhibitors of pinocytosis of human beta-glucuronidase by human fibroblasts. The larger molecular weight polyphosphomonoester fragment is 100,000-fold more potent an inhibitor of enzyme uptake than the smaller penta-mannosyl-monophosphate fragment. Binding to attached fibroblasts at 3 degrees C was much greater with the polyphosphomonoester fragment than with the pentamannosyl-monophosphate. The larger molecular weight fragment was also subject to adsorptive pinocytosis and was taken up by fibroblasts at a rate 30- fold greater than the rate of uptake of pentamannosyl-monophosphate. Evidence that the polyphosphomonoester fragment is taken up by the phosphomannosyl-recognition system that mediates uptake of lysosomal enzymes includes: (a) its pinocytosis is inhibited by the same compounds that competitively inhibit enzyme pinocytosis (mannose-6-phosphate and phosphomannan from saccharomyces cerevisiae mutant mnn-1); (b) alkaline phosphatase treatment greatly reduces its susceptibility to pinocytosis; (c) its pinocytosis is competitively inhibited by high-uptake human beta-glucuronidase; and (d) this inhibition by high-uptake enzyme is dramatically reduced by prior treatment of the enzyme with alkaline phosphatase or endoglycosidase-H. Endoglycosidase-H treatment human beta-glucuronidase dramatically reduced its susceptibility to pinocytosis by fibroblasts. The phosphomannosyl components of high- uptake enzyme released by endoglycosidase-H treatment were much less effective inhibitors of polyphosphomonoester pinocytosis than when present on the phosphomannyl-enzyme. These results suggest that high-uptake acid hydrolases may be polyvalent ligands analogous to the polyphosphomonoester mannan fragment whose pinocytosis depends on interaction of more than one phospho-mannosyl recognition marker with pinocytosis receptors on fibroblasts.

Natural phosphorylation of group A streptococcal pyrogenic exotoxin type C

Group A streptococcal pyrogenic exotoxin (SPE) type C, produced by strain T18P grown in the presence of 32P, was separated from culture supernatant fluids by using alcohol precipitation. The resulting toxin (EtOH-1) contained 3 X 10(6) to 5 X 10(6) cpm of 32P per milligram of protein. The radiolabel migrated with SPE C during isoelectric focusing in polyacrylamide gels (pI 6.7) and double immunodiffusion, in which the toxin formed a line of identity with highly purified SPE C when reacted with hyperimmune antisera raised against SPE C. The EtOH-1 radiolabeled toxin was pyrogenic and had the capacity to enhance host susceptibility to lethal endotoxin shock. EtOH-1 toxin lost both radiolabel and biological activity after being treated with alkaline phosphatase. The nonspecific lymphocyte mitogenicity of purified unlabeled SPE C was stimulated by adenosine monophosphate but not adenosine, adenosine diphosphate, or adenosine triphosphate. Adenosine monophosphate may function as a cofactor of SPE C and contribute the phosphate group required for biological activity.

Spectrin rearrangement early in erythrocyte ghost endocytosis

The endocytic vacuoles induced in white ghosts were found to be depleted of spectrin and therefore it was proposed that they arose from spectrin-free areas in the erythrocyte membrane. To follow changes in spectrin distribution during endocytosis, affinity-purified rabbit antispectrin antibodies were produced. Quantitative techniques were developed for the use of a highly specific 125I-F(ab')2 antispectrin, and these showed that before the appearance of vacuoles, as assessed by phase microscopy, there was a reproducible decrease in immunoreactive spectrin. To determine whether this spectrin decrease represented a local or diffuse spectrin loss or a spectrin rearrangement, morphologic studies were undertaken using transmission electron microscopy on samples treated with rabbit antispectrin and ferritin-conjugated goat anti-rabbit immunoglobulin. These studies showed that endocytosis was preceded by the creation of extensive spectrin-free areas separated by discrete spectrin-containing zones. Pretreatment of ghosts with alkaline phosphatase blocked all forms of endocytosis and prevented the creation of spectrin-free areas. Therefore, it is proposed that under the impetus of endocytosis inducers, phosphorylated spectrin is redistributed so that spectrin-free zones are created, and that endocytic vacuoles form and fuse in spectrin-free areas.

A comparison of different enzyme-antibody conjugates for enzyme-linked immunosorbent assay

Calf intestinal alkaline phosphatase (CIAP)- and horseradish peroxidase (HRP)-linked goat antibody (Ab) conjugates have been prepared by two procedures. One procedure is by glutaraldehyde coupling of the proteins; the other is by intermolecular disulfide bond formation of the appropriately modified proteins. The conjugates, specific for rabbit IgG, were tested for their effectiveness as reagents in enzyme-linked immunosorbent assays for ragweed antigen E specific rabbit antibody. The CIAP-Ab conjugate prepared by glutaraldehyde coupling and the HRP-Ab conjugate made by disulfide bond formation were equally effective reagents for immunoassay, but the HRP-Ab conjugate obtained by glutaraldehyde coupling was definitely less useful than the other two conjugates. The assay procedure utilized an antigen E coupled paper disc as the immunosorbent and it was sensitive in the range of 0.5--100 ng per test. Inhibition of the enzyme-linked immunosorbent assay was used as a sensitive technique for measuring antigenic activity of antigen E or its derivatives.

Recognition of human urine alpha-N-acetylglucosaminidase by rat hepatocytes. Involvement of receptors specific for galactose, mannose 6-phosphate and mannose

Adsorptive endocytosis of alpha-N-acetylglucosaminidase from human urine by isolated rat hepatocytes is inhibited by glycoproteins, polysaccharides and sugars that are known to bind to cell-surface receptors specific for either terminal galactose/N-acetylgalactosamine residues, terminal mannose residues or mannose 6-phosphate residues. Recognition of alpha-N-acetylglucosaminidase by a cell-surface receptor specific for terminal galactose/N-acetylgalactosamine residues is supported by the observations (a) that neuraminidase pretreatment of the enzyme enhances endocytosis, (b) that beta-galactosidase treatment decreases endocytosis and (c) that neuraminidase pretreatment of hepatocytes decreases alpha-N-acetylglucosaminidase endocytosis. Recognition of alpha-N-acetylglucosaminidase via receptors recognizing mannose 6-phosphate residues is lost after treatment of the enzyme with alkaline phosphatase and endoglucosaminidase H. The effect of endoglucosaminidase H supports the view that the mannose 6-phosphate residues reside in N-glycosidically linked oligosaccharide side chains of the high-mannose type. The weak inhibition of endocytosis produced by compounds known to interact with cell-surface receptors specific for mannose residues suggests that this recognition system plays only a minor role in the endocytosis of lysosomal alpha-N-acetylglucosaminidase by hepatocytes.

Isoelectric focusing of acid hydrolases in human fibroblasts and leucocytes

Lysosomal hydrolases in fibroblasts and leucocytes exhibited the same isoelectric focusing pattern as found in liver. Treatment with neuraminidase had a great effect on the pattern of several glycosidases while treatment with alkaline phosphatase did not significantly change the pattern. These findings are discussed with special reference to the different "uptake" systems that exist for acid hydrolases.

Characteristics of a low-molecular-weight factor extracted from mouse tumors that affects in vitro properties of macrophages

A dialysable low-molecular-weight factor capable of affecting in vitro properties of macrophages was extracted from four different mouse tumors. This factor not only modulates closely related properties of peritoneal macrophages such as spreading and migration but also inhibits lipopolysaccharde-induced tumoricidal activity of these cells. It can be extracted not only from tumor tissues but also from tumor cells grown in vitro. The appearance of this factor is unique to tumors and it is not present in detectable quantities in normal tissues. The factor from one of the tumors, Lewis lung carcinoma, was purified extensively and the partially purified factor retains all the above effects on macrophages. It is not sensitive to pronase or a mixture of bovine spleen phosphodiesterase II, E. coli alkaline phosphatase and pancreatic ribonuclease. The factor is lipid-like in character and it is soluble in both organic solvents and aqueous media. It has ionizable group(s) and is anionic at neutral pH but non-ionic under acidic conditions.

Human transfer factors: structural properties suggested by HPRP chromatography and enzymatic sensitivities

Leukocyte extracts containing human transfer factor (TF) were fractionated by exclusion chromatography, and the active fraction (Sephadex G25, Fraction IIIa) was subjected to high pressure, reverse phase (HPRP) chromatography and enzymatic degradation. TF activity was assessed by the systemic transfer of dermal skin test reactivity from KLH-immunized donors to naive recipients. Preparative HPRP chromatography resolved Fraction IIIa into multiple chromophoric regions, two of which demonstrated transfer of KLH reactivity. Alkaline phosphatase treatment of Fraction IIIa converted the major ultraviolet-absorbing component, 5'-inosine monophosphate, to inosine and resulted in TF activity being restricted to one region. This HPRP region (R1A) contained less than 1% of the UV254 active material in Fraction IIIa but greater than 90% of the reactivity. The sensitivity of TF to pronase, proteinase K, phosphodiesterase I, and phosphodiesterase II was evaluated by inhibition of systemic transfer of KLH reactivity. Pronase and proteinase K destroyed systemic transfer activity and the pronase destruction could be inhibited with traysylol. Phosphodiesterase I, a 3' exonuclease, destroyed activity, whereas phosphodiesterase II, a 5' exonuclease, did not. The data are consistent with a phosphodiester-containing polypeptide in the structure of human TF for KLH reactivity.

Evaluation of several enrichment procedures for the isolation of recombinant plasmid DNA

A number of methods for the selective enrichment of recombinant plasmids were examined; these include alkaline phosphatase treatment of the restricted pBR322 vector, as well as a combination of this and S1 nuclease treatment of the ligated mixture of pBR322 and pCR1 plasmids or S. griseus DNA followed by D-cycloserine treatment to enrich for cells carrying recombinant molecules. The relative efficiencies of these methods were compared.

Histochemical localization of adenosine triphosphatase activity in bovine ruminal epithelium

A fine-structural histochemical technique was used to localize magnesium-dependent adenosine triphosphatase (Mg-ATPase) activity in ruminal mucosa. Precipitate appeared on the cytoplasmic surface of the plasmalemma in cells of the upper stratum spinosum, the stratum granulosum, and the deepest layer of the stratum corneum. This ATPase activity was sensitive to glutaraldehyde fixation and possibly to ouabain, but was unaffected by sodium and potassium. The preponderance of Mg-ATPase activity in bovine ruminal epithelium may make it impossible to detect sodium-potassium-activated adenosine triphosphatase ((Na + K)-ATPase) activity histochemically. A Mg-ATPase activity also occurred in mitochondria of the stratum spinosum and stratum granulosum. None of the ruminal sections hydrolyzed adenosine diphosphate, inosine triphosphate, or beta-glycerophosphate when these compounds were used as substitute substrates for adenosine triphosphate. When adenosine-5'-monophosphate was the available substrate, a reaction product appeared in the same layers as Mg-ATPase activity, but the reaction product was confined to the intercellular space.

L-Glutamate decarboxylase

Much progress has been made in recent years regarding enzymological aspects of mammalian brain GAD, such as its purification and characterization, but some uncertainty still remains concerning its molecular weight and forms, and its subunit structure. The availability of antibodies to this enzyme has allowed immunocytochemical studies which have provided important information on the intrinsic organization of GABA-ergic neurones in the CNS, particularly in the cerebellum and nigrostriatal pathway. With the increased understanding of the enzymology of GAD and the distribution of central GABA-ergic neurones, it is becoming feasible to study the regulatory biochemistry of GAD in terms of control and adaptive mechanisms at the cellular level. In our own laboratory, as well as in others, initial approaches have already begun. Obviously, cellular regulation of this phenotypic enzyme is an important issue for the understanding of GABA-ergic neurones and their functions.

Effect of anti-spectrin antibody and ATP on deformability of resealed erythrocyte membranes

Deformability of resealed erythrocyte membranes was measured by using an ektacytometer. Divalent anti-spectrin antibody, but not monovalent anti-spectrin Fab fragments, decreased membrane deformability. Membranes resealed with MgATP were more deformable than those without MgATP. Exogenous alkaline phosphatase, which dephosphorylates spectrin, decreased membrane deformability. These results suggest that spectrin is an essential component of the system that determines erythrocyte deformability. They are consistent with the view that the role of ATP in membrane deformability is mediated through phosphorylation of the spectrin.

Amount and properties of uptake forms in preparations of alpha-mannosidase from pig kidney

alpha-Mannosidase (alpha-D-mannoside mannohydrolase, EC 3.2.1.24) from pig kidney has been shown to exist in multiple forms differing in their capability to be endocytosed by alpha-mannosidase deficient cultured cells. A method is presented to evaluate the amount of "uptake" forms in different preparations of the enzyme. Preparations with different rates of uptake were shown to contain different amount of "uptake" forms and "non-uptake" forms. The content of "uptake" forms in a preparation was identical with that of enzyme molecules bearing a phosphorylated carbohydrate group necessary for the recognition by cell surface receptors.

Evidence for lysosomal enzyme recognition by human fibroblasts via a phosphorylated carbohydrate moiety

Adsorptive endocytosis of five different lysosomal enzymes from various human and non-human sources was susceptible to inhibition by mannose and l-fucose, methyl alpha-d-mannoside, alpha-anomeric p-nitrophenyl glycosides of mannose and l-fucose, mannose 6-phosphate and fructose 1-phosphate. A few exceptions from this general scheme were observed for particular enzymes, particularly for beta-glucuronidase from human urine. The inhibition of alpha-N-acetylglucosaminidase endocytosis by mannose, p-nitrophenyl alpha-d-mannoside and mannose 6-phosphate was shown to be competitive. The loss of endocytosis after alkaline phosphatase treatment of lysosomal enzymes supports the hypothesis that the phosphorylated sugars compete with a phosphorylated carbohydrate on the enzymes for binding to the cell-surface receptors [Kaplan, Achord & Sly (1977) Proc. Natl. Acad. Sci. U.S.A.74, 2026-2030]. Endocytosis of ;low-uptake' forms of alpha-N-acetylglucosaminidase and alpha-mannosidase was likewise susceptible to inhibition by sugar phosphates and by alkaline phosphatase treatment, suggesting that ;low-uptake' forms are either contaminated with ;high-uptake' forms or are internalized via the same route as ;high-uptake' forms. The existence of an alternative route for adsorptive endocytosis of lysosomal enzymes is indicated by the unaffected adsorptive endocytosis of rat liver beta-glucuronidase in the presence of phosphorylated sugars and after treatment with alkaline phosphatase.