Chitosan gels: 2. Mechanism of gelation

The gelation behaviour of solutions of chitosan on treatment with acyl anhydrides has been studied. The degree of $\text{N-}\text{acylation}$ required to initiate geletion has been found to depend on the molecular weight of the acyl anhydride and the concentration of chitosan, but to be independent of temperature. The energy of activation of $\text{N-}\text{acylation}$ has been determined for $\text{N-}\text{acetylation}$ and $\text{N-}\text{henoylation}$. A mechanism has been proposed for the gelation process.     

Emission-wavelength-dependent decay of the fluorescent probe N-phenyl-1-naphthylamine

We have measured the fluorescence decay of $\text{N-}\text{phenyl}\text{-1-}\text{naphthylamine}$ using the phase-modulation method, in several solvent systems and egg phosphatidylcholine vesicles. The decay is monoexponential in pure solvents (both polar and non-polar) of low viscosity. In polar viscous solvents or in non-polar solvents containing an added polar solute, the decay is heterogeneous and emission wavelength dependent. In such cases, dielectric relaxation and/or excited-state complexing give rise to a shift of the emission spectrum on the nanosecond time scale. Emission-wavelength-dependent decay was also observed when $\text{N-}\text{phenyl}\text{-1-}\text{naphthylamine}$ was bound to egg phosphatidylcholine vesicles. From these results as well as the position of the emission spectral maximum, we conclude that $\text{N-}\text{phenyl}\text{-1-}\text{naphthylamine}$ probes the ester-carbonyl region of the phospholipid acyl chains, where it undergoes an excited-state reaction. This result contradicts the often made assumption that $\text{N-}\text{phenyl}\text{-1-}\text{naphthylamine}$ probes the deeper hydrocarbon region of the bilayer.     

Enantiomer selection in the nucleophilic addition reaction of optically active amines to α-amino acid N-carboxyanhydrides

The enantiomer selection in the nucleophilic addition reaction of optically active amines such as α-amino acid esters to phenylalanine and $\text{N-}\text{methylphenylalanine}\text{N-}\text{carboxyanhydride}$ in $\text{m-}\text{dimethoxybenzene}$ as a solvent has been investigated. Stereoselectivity between the amines and the $\text{N-}\text{carboxyanhydrides}$ was found to change markedly according to the reaction conditions. This experimental finding is in contrast to the idea hitherto accepted that in the nucleophilic addition-type polymerization of α-amino acid $\text{N-}\text{carboxyanhydride}$ the growing chain end reacts preferentially with one of the enantiomorphic $\text{N-}\text{carboxyanhydrides}$ having the same configuration, and indicates the importance of the investigation of stereoselectivity in the $\text{N-}\text{carboxyanhydride}$ polymerization using suitable model reactions. Most $\text{(S)-α-}\text{amino}$ acid esters reacted preferentially with $\text{(R)-}\text{phenylalanine}\text{N-}\text{carboxyanhydride}$, and this type of stereoselectivity increased with the $\text{N-}\text{methylation}$ of $\text{N-}\text{carboxyanhydride}$ and with increasing bulkiness of the C^α substituent of α-amino acid esters (alanine < norleucine < leucine < valine). The relationship observed between the stereoselectivity and the structures of amines and $\text{N-}\text{carboxyanhydrides}$ was explained satisfactorily in terms of the transition state model in which the interaction of $\text{N-}\text{carboxyanhydride}$ nitrogen and α-amino acid ester carbonyl as well as the interaction of $\text{N-}\text{carboxyanhydride}$ carbonyl and α-amino acid ester nitrogen was taken into account. $\text{(S)-}\text{Proline}$ ethyl ester did not show enantiomer selectivity toward phenylalanine $\text{N-}\text{carboxyanhydride}$, but reacted preferentially with $\text{(S)-(N)-}\text{methylphenylalanine}\text{N-}\text{carboxyanhydride}$. for the reaction of proline ester with $\text{N-}\text{carboxyanhydride}$ a transition-state model was proposed, which was different from the transition state model proposed for other α-amino acid esters. Some experiments were carried out to examine the transition-state models proposed. The implications of the present investigation in stereoselectivity in the nucleophilic addition-type polymerization of $\text{N-}\text{carboxyanhydride}$ hitherto reported are discussed.     

Effect of N-ethylmaleimide on leucine transport in the chang liver cell. II. Effect on the kinetics of Na+-independent transport

The Na⁺-independent leucine transport system is resolved into two components by their different affinity ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ about 44 μM and 8.0 mM) for leucine in the Chang liver cell. Treatment of the cells with $\text{N-}\text{ethylmaleimide}$ (1 mM) specifically stimulates the high-affinity component of the Na⁺-independent system by greatly increasing its $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ value, whereas the $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ value of the low-affinity component is markedly lowered. The stimulatory effect of $\text{N-}\text{ethylmaleimide}$ on leucine transport is reduced by prior treatment of the cells with 2,4-dinitrophenol, but this phenomenon seems to be irrelevant to the ATP-depleting action of the uncoupler. The treatment with 2,4-dinitrophenol has been found not to be inhibitory on the subsequent Na⁺-independent leucine uptake itself. Treatment with dibucaine, a phospholipid-interacting drug, also reduces to varying degrees (depending on its concentration) the stimulatory effect of $\text{N-}\text{ethylmaleimide}$ on the subsequent leucine uptake, although pretreatment with dibucaine can stimulate the Na⁺-independent leucine uptake itself. We conclude that the stimulatory effect of $\text{N-}\text{ethylmaleimide}$ on leucine transport is not correlated with the energy level of cell, but involves the perturbation of the membrane bilayer structures.     

Inhibition of urea synthesis by pent-4-enoate associated with decrease in N-acetyl-L-glutamate concentration in isolated rat hepatocytes

Pent-4-enoate at 0.1 to 1.0 mM strongly inhibited urea synthesis in isolated rat hepatocytes. Pent-4-enoate at the same concentrations markedly decreased concentrations of $\text{N-}\text{acetyl-}\text{L}\text{-glutamate}$, an essential activator of carbamoyl-phosphate synthase-I (EC 2.7.2.5), and the decrease was well parallel with the inhibition of urea synthesis by pent-4-enoate. This compound also lowered cellular concentrations of acetyl-CoA, a substrate of acetylglutamate synthase (EC 2.3.1.1). Pent-4-enoate in a dose of 1 mM did not significantly affect cellular concentrations of ATP, and had no direct effect on acetylglutamate synthase activity. These results suggest that the inhibition of urea synthesis by pent-4-enoate is due to decrease in $\text{N-}\text{acetyl-}\text{L}\text{-glutamate}$ concentration and that the decrease is probably brought about by decreased rate of its synthesis due to the lowered concentration of cellular acetyl-CoA.     

Effect of N-ethylmaleimide on leucine transport in chang liver cells. I. Stimulatory effect on Na+-independent transport at low concentrations of leucine

Pretreatment of Chang liver cells with $\text{N-}\text{ethylmaleimide}$ (0.5 or 1 mM) stimulated Na⁺-independent uptake of leucine at low concentrations (?1 mM). The stimulatory effect of $\text{N-}\text{ethylmaleimide}$ on the uptake of leucine measured in Na⁺-replete medium was completely blocked by the addition of $\text{b-2-}\text{aminobicyclo}\text{[2,2,1]}\text{heptane}\text{-2-}\text{carboxylate}$ (5 mM), which shows that the L system participates in the stimulation. The Na⁺-dependent uptake of glycine was depressed by $\text{N-}\text{ethylmaleimide}$ pretreatment. The stimulation of the Na⁺-independent component of leucine uptake continued for at least 30 min after $\text{N-}\text{ethylmaleimide}$ treatment, while the inhibition of glycine uptake was progressive with time and the Na⁺-dependent uptake of leucine became depressed later, after the treatment. It has been demonstrated that treatment of cells with $\text{N-}\text{ethylmaleimide}$ is capable of increasing the Na⁺-independent influx of leucine and at the same time slightly decreasing the efflux of it. These results suggest that $\text{N-}\text{ethylmaleimide}$ attacks the Na⁺-independent system of amino acid transport at the reactive SH groups(s) of relevant protein(s) in favor of specific activation of that system in this cell.     

Amino acid uptake by yeasts: IV. Effect of thiol reagents on l-leucine transport in Saccharomyces cerevisiae

(1) $\text{N-}\text{Ethylmaleimide}$ (a penetrating SH- reagent) inactivated l-[¹⁴C]leucine entrance (binding and translocation) into Saccharomyces cerevisiae, the extent of inhibition depending on the time of preincubation with $\text{N-}\text{ethylmaleimide}$, $\text{N-}\text{ethylmaleimide}$ concentration, the amino acid external and internal concentration, and the energization state of the yeast cells. With d-glucose-energized yeast, $\text{N-}\text{ethylmaleimide}$ inhibited l-[¹⁴C]leucine entrance in all the assayed experimental conditions, but with starved yeast and low (0.1 mM) amino acid concentration, it did not inhibit l-[¹⁴C]leucine binding, except when the cells were preincubated with l-leucine. With the rho^? respiratory-deficient mutant (energized cells), $\text{N-}\text{ethylmaleimide}$ inhibited l[¹⁴C]leucine entrance as with the energized wild-type, though to a lesser extent. (2) Analysis of the $\text{N-}\text{ethylmaleimide}$ effect as a function of l-[¹⁴C]leucine concentration showed a significant decrease of $\text{J}{}_{\mathrm{<mtext>max</mtext>}}$ values of the high- (S₁) and low- (S₂) affinity amino acid transport systems, but $\text{K}{}_{\mathrm{<mtext>T</mtext>}}$ values were not significantly modified. (3) When assayed in the presence of d-glucose, $\text{N-}\text{ethylmaleimide}$ inhibition of d-glucose uptake and respiration contributed significantly to inactivation of l-[¹⁴C]leucine entrance. Pretreatment of yeast cells with 2,4-dinitrophenol enhanced the effect of l-[¹⁴C]leucine binding and translocation. (4) Bromoacetylsulfanilic acid and bromoacetylaminoisophthalic acid, two non-penetrating SH- reagents, did not inactivate l-[¹⁴C]leucine entrance, while $\text{p-}\text{chloromercuribenzoate}$, a slowly penetrating SH- reagent, inactivated it to a limited extent. When compared with the effect of $\text{N-}\text{ethylmaleimide}$, these negative results indicate that thiol groups of the l-[¹⁴C]leucine carrier were not exposed on the outer surface of the yeast cell permeability barrier.     

Glycoprotein characteristics of the sodium channel saxitoxin-binding component from mammalian sarcolemma

The saxitoxin-binding component of the excitable membrane sodium channel exhibits glycoprotein characteristics as evidenced by its specific interaction with various agarose-immobilized lectins. The detergent-solubilized saxitoxin-binding component interacts quantitatively with immobilized wheat germ agglutinin and concanavalin A and fractionally with immobilized Lens culinaris hemagglutinin and Ricinus communis agglutinin. These lectins preferentially bind $\text{N-}\text{acetylglucosamine}$ and sialic acid (wheat germ agglutinin), mannose (concanavalin A and Lens cunilaris and galactose (Ricinus communis). Removal of terminal sialic acid residues by neuraminidase markedly decreases binding to immobilized wheat germ agglutinin but uncovers sites capable of interacting with lectins specific for galactose and $\text{N-}\text{acetylgalactosamine}$. $\text{β-N-}\text{acetylglucosaminidase}$, an exoglycosidase has no effect on the binding of the channel protein to wheat germ agglutinin. Similarly, phospholipase C has no effect on binding of the solubilized toxin binding component to this lectin. Neither wheat germ agglutinin nor concanavalin A free in solution alters the number of toxin binding sites or their affinity for toxin. The sodium channel saxitoxin-binding component appears to be a glycoprotein containing terminal sialic acid residues and internal mannose, galactose, $\text{N-}\text{acetylglucosamine}$, and $\text{N-}\text{acetylgalactosamine}$ residues. The toxin binding site is spatially separated from the binding sites for the lectins studied. The effect of these sugar moieties must be considered when evaluating the biophysical parameters of the sodium channel.     

Membrane lipid modifications: Biosynthesis and identification of phosphatidyl-N-methyl-N-isopropylethanolamine in rat liver microsomes

In previous studies on the modification of polar head groups of membrane phospholipids with the unnatural base analog, $\text{N-}\text{isopropylethanolamine}$, we reported an unidentified phospholipid in addition to $\text{phosphatidyl}\text{-N-}\text{isopropylethanolamine}$ in the various membrane fractions of rat liver. The structure of this phospholipid has now been identified as $\text{phosphatidyl}\text{-N-}\text{methyl}\text{-N-}\text{isopropylethanolamine}$ by nuclear magnetic resonance spectroscopy, and by chromatographic and enzymic analysis. In addition, we found that when rats were injected intraperitoneally with the $\text{N-}\text{methyl}\text{-N-}\text{isopropylethanolamine}$, 19% of teh liver microsomal phospholipid was $\text{phosphatidyl}\text{-N-}\text{methyl}\text{-N-}\text{isopropylethanolamine}$.     

Cuticular strength and pigmentation of rust-red and black strains of Tribolium castaneum: Correlation with catecholamine and β-alanine content

Rust-red wild and black mutant strains of the red flour beetle, Tribolium castaneum, were used to investigate temporal patterns of catecholamine and β-alanine content during sclerotization and pigmentation of adult cuticle and to relate these patterns to corresponding changes in cuticle resistance to puncture. Rust-red elytral cuticle sclerotized more rapidly than black cuticle until 6 days after adult eclosion when both became equal in puncture resistance. The cuticular concentrations of $\text{N-β-}\text{alanyldopamine}$ (NBAD), β-alanine and 3,4-dihydroxyphenylacetic acid (DOPAC) increased more rapidly in the rust-red strain than in the black strain during the first 7 days following adult eclosion. Conversely, cuticular dopamine increased more rapidly in black than in the red strain. Thus the rust-red pigmentation and rapid sclerotization appear to be related to the availability of β-alanine, $\text{N-β-}\text{alanyldopamine}$ and DOPAC. Melanization was prevented and rust-red pigmentation induced by injections of β-alanine or NBAD into newly ecdysed black mutant beetles. Crosses of the two strains generally had intermediate levels of cuticular dopamine and β-alanine, but the NBAD levels were similar to those of the rust-red strain. Dopamine, NBAD and DOPAC levels became similar in both black and rust-red strains about 6 days after adult ecdysis as did resistance to puncture. Therefore, dopamine appears to be directed initially into the melanin pathway in black adults due to a temporary lack of $\text{N-}\text{acylation}$ with β-alanine. After the melanization phase, dopamine is metabolized to sclerotization precursors eventually resulting in normal physical properties of the exoskeleton.     

Enzymatic continuous production of N-acetyl-l-methionine from N-acetyl-dl-methioninamide with Erwinia carotovora containing a new amidase activity

A procedure for production of $\text{N-}\text{acetyl-}\text{l}\text{-methionine}$ ($\text{N-}\text{Ac-}\text{l}\text{-Met}$) from its racemic mixture by enzymatic continuous hydrolysis of the l-enantiomer of $\text{N-}\text{acetyl-}\text{dl}\text{-methioninamide}$ ($\text{N-Ac-}\text{dl}\text{-Met · NH}{}_2$) is described. For this hydrolysis, whole cells of Erwinia carotovora immobilized by κ-carrageenan gel were employed. The complete conversion of $\text{N-}\text{Ac-}\text{dl}\text{-Met · NH}{}_2$ to $\text{N-}\text{Ac-}\text{l}\text{-Met}$ was achieved by using a column packed with the immobilized cells. The half-life of the enzyme activity of the column was calculated to be ～100 days. Pure crystalline $\text{N-}\text{Ac-}\text{l}\text{-Met}$ was readily isolated from the effluent with >87.5% yield. $\text{N-}\text{Ac-}\text{d}\text{-Met · NH}{}_2$ was easily racemized by incubating in ethanol containing 0.1 m NaOH for 30 min at 80°C, and used again for substrate.     

Evaluation on the hydrolysis of methylumbelliferyl-tetra-N-acetylchitotetraoside by various glucosidases. A comparative study

• 1.1. In human plasma, an enzyme is present which hydrolyzes 4-methylumbelliferyl-tetra-N-acetylchitotetraoside. The function of this enzyme is unknown.
• 2.2. We have examined whether hyaluronidase, neutral endoglucosaminidase, $\text{N-}\text{acetyl}\text{-β-}\text{d}\text{-}\text{hexosaminidase}$, aspartylglucosaminidase, β-d-glucosidase, and chitobiase could hydrolyze MU-TACT. The results obtained are detailed below.
• 3.3. A purified commercial preparation of hyaluronidase does not hydrolyze MU-TACT.
• 4.4. Substrate specificity requirements, pH optimum and subcellular localization indicate that neutral endoglucosaminidase is distinguishable from MU-TACT hydrolase. Also commercial neutral endoglucosaminidase D and H have no affinity towards MU-TACT.
• 5.5. $\text{N-}\text{Acetyl}\text{-β-}\text{d}\text{-}\text{hexosaminidase}$ is different from MU-TACT hydrolase for the following reasons: (a) a purified enzyme preparation does not hydrolyze MU-TACT; (b) there is no correlation in the activity of the enzymes; (c) MU-TACT hydrolase is not deficient in cells of a patient with a deficiency of total $\text{N-}\text{acetyl}\text{-β-}\text{d}\text{-}\text{glucosaminidase}$; and (d) the 2 enzymes have very different Chromatographic characteristics and Con A binding properties.
• 6.6. Enzyme characteristics, substrate structural requirements and a lack of correlation with MU-TACT hydrolase activity suggest that aspartylglucosaminidase, β-d-glucosidase, and chitobiase are not involved in the hydrolysis of MU-TACT.
• 7.7. None of the enzymes which we have considered corresponds to MU-TACT hydrolase. The exact nature and the function of the enzyme remains an enigma.

     

Cytotoxicity of pyocin S2 to tumor and normal cells and its interaction with cell surfaces

Cytotoxicity and adsorption of pyocin S2 produced by Pseudomonas aeruginosa M47 (PAO 3047) to virally transformed mammalian cells, human malignant cells and normal cells in the same species were studied. Pyocin S2 inhibited the growth of not only tumor cells (XC, TSV-5, mKS-A TU-7, HeLa-S3 and AS-II cells) but also normal cells (BALB/3T3 and BHK 21 cells). The inhibitory effects on the cells increased with an increase of pyocin S2 activity. On the other hand, there were some tumor cells (155-4 T2 and HGC-27 cells) and normal cells (normal rat kidney and human embryo lung cells) which were resistant to pyocin S2. The pyosin S2 activity was neutralized by the cell membrane preparations from pyosin S2-sensitive cells, but not by those from pyocin-resistant cells. This neutralization ability was inhibited by high concentrations of D-galactose, $\text{N-}\text{acetyl-}\text{D}\text{-galactosamine and}\text{N-}\text{acetyl}$ neuraminic acid and completely destroyed by periodate and neuraminidase. The inhibition by the saccharides was concentration dependent. These results suggest that the toxicity of pyocin S2 to several mammalian cells is due to the presence of the binding site for pyocin S2 in the cell membrane and further, that the carbohydrate moiety, especially of D-galactose, $\text{N-}\text{acetyl-}\text{D}\text{-galactosamine}$ and sialic acid, may play an important role as an initial binding site for pyocin S2.     

The study of rous sarcoma virus-transformed baby hamster kidney cells using fluorescent probes

The fluorescent probes pyrene, pyrene butyric acid and $\text{N-}\text{phenyl}$ 1-naphthylamine have been used to investigate the changes that accompany in vitro transformation of a baby hamster kidney cell line using Rous sarcoma virus. The fluorescent probes which reside in the membrane were used to compare the changes in microviscosity and polarity of the membranes of normal cells with two transformed cell lines. The spectrofluorimetric data indicate that following transformation the probe $\text{N-}\text{phenyl}$ 1-naphthylamine resides in a more polar environment. However, using the probe pyrene, the yield of excimer indicates decreased mobility of this probe in the membrane of transformed cells. The data also indicate differences between the two transformed cell lines. Laser photolysis was used to study the lifetime of the pyrne probes and the quenching of the pyrene fluorescence in the membrane by several different quenching molecules. The data indicate differences between the three cell lines and suggest that transformation decreases movement within the membrane.     

A statistical mechanical treatment of fatty acyl chain order in phospholipid bilayers and correlation with experimental data. B. Dipalmitoyl-3-sn-phosphatidylcholine

In order to help bridge the conceptual gap between experimental data on chains of phospholipid molecules and their microscopic organization, a theoretical model has been proposed in a preceding paper. The intentions associated with the new theory were to describe a model able to reproduce accurately the experimental data. This capability is essential to monitor some of the mechanisms behind the physical data. The results presented here show first that, provided a suitable fitting of the phenomenological parameters entailed in the model, the theory indeed gives good agreement with experimental data (²H-NMR, neutron scattering, calorimetry) obtained for a $\text{dipalmitoyl}\text{-3-sn-}\text{phosphatidylcholine}$ bilayer. This property of the model is then specifically used to describe the nature of the perturbing effects of local anaesthetics and cholesterol on the organization of the acyl chains and to correlate these effects with the experimental data. Finally the theoretical model is used to supplement experimental data by describing the acyl chain organization in terms of the most probable spectrum of chain conformations. Predictions are made about the one-, two- and three-dimensional mean spatial characteristics of the acyl chains.     

Studies on the fragmentation of erythrocyte ghost membrane with p-chloromercuribenzoate in the micromolar range

The effects of nonsaturating amounts (5–60 nmol/mg membrane protein) of $\text{p-}\text{chloromercuribenzoate}$ on the stability of unsealed erythrocyte ghosts were studied by turbidimetric measurements and direct observation by phase contrast microscopy. The organic mercurial provokes drastic disorganization of the membrane involving vesicle formation by inter- and externalization of the bilayer. These effects are not associated with a release in solution of membrane proteins which was shown in previous studies to occur at higher $\text{p-}\text{chloromercuribenzoate}$ concentration. Attempts have been made to identify the proteins involved in this phenomenon by the use of nonsaturating amounts of radioactively-labelled $\text{p-}\text{chloromercuribenzoate}$. Actin and band 3 protein which are the first to be labelled, represent plausible candidates as sensitive targets for the disrupting organic mercurial. Stroma obtained from spherocytes did not show significant differences with normocytes in their stability with regard to $\text{p-}\text{chloromercuribenzoate}$. Other reagents including $\text{N-}\text{ethylmaleimide}$, diamide and DNAase I were also studied. The results suggest strongly that the integrity of the sulfhydryl groups of actin, as well as those of band 3 protein, is essential for the stability of the erythrocyte membrane.     

The solubilization of cytoskeletons of human erythrocyte membranes by p-mercuribenzene sulphonate

The disruption of erythyrocyte membrane cytoskeletons brought about by treatment with $\text{p-}\text{mercuribenzene sulphonate}$ (PMBS) has been followed by measurements of turbidity and the binding of ²⁰³Hg-labelled PMBS. After pretreatment with $\text{N-}\text{ethylmaleimide}$ to block readily reactive sulphydryl groups, incubation with [²⁰³Hg]PMBS showed incorporation of approximately 4 moles radiolabel per mole of spectrin and one per mole of actin. The incorporation of radiolabel paralleled the decrease in turbidity, and the labelling of spectrin paralleled that of actin. The kinetics were pseudo first order, and the pH dependence of the observed rate constant indicated a normal $\text{p}\text{K}{}_{\mathrm{<mtext>a</mtext>}}$ value for the sulphydryl group involved. The calculated second-order rate constant for the reaction of the sulphydryl anion with PMBS, however, was several orders of magnitude less than expected from model compound studies. The results suggest that association between spectrin and actin may result in the steric hindrance of reactivity of a limited number of sulphydryl groups in each protein. Disruption of the spectrin-actin association may then be linked to the modification of the sulphydryl groups.     

The linkage of teleost skin keratan sulfate to protein

The linkage of teleost skin keratan sulfate to protein was investigated. Afeter its exhaustive digestion with pronase, peptidokeratan sulfate was obtained with aspartic acid as the predominant amino acid. The N-terminal of the amino acid residues of the preparation was dansylated, and the carbohydrate-peptide linkage fragment was isolated, with the aid of fluorescence, by sequential digestion with Flavobacterium endo-β-galactosidase, β-galactosidase, β-N-acetylhexosaminidase and endo-β-N-acetylglucosaminidase D, followed by Bio-Gel p-4 column chromatography. The structure of the dansylated fragment thus obtained was identified dansylated asparaginyl $\text{N-}\text{acetyl-}\text{D}\text{-glucosamine}$. Treatment of the dansylated keratan sulfate peptide with almond glycopeptidase, which specially cleaves thet asparaginyl $\text{N-}\text{acetyl-}\text{D}\text{-glucosamine}$ linkage in the glycoproteins, also showed asparaginyl $\text{N-}\text{aceytyl-}\text{D}\text{-glucosamine}$ linkage to be in the core region of this keratan sulfate. We conclude that teleost skin keratan sulfate is bound to protein via an N-glycosyl linkage between $\text{N-}\text{acetyl-}\text{D}\text{-glucosamine}$ and asparagine. The keratan sulfate core apparently consist of trimannosyl-N,N′-diacetylchitobiose units, considering the specificity of endo-β-N-acetylglucosaminidase D.     

Errata

Optimal conditions for activation of adenylate cyclase in membrane particles were studied. Enzyme activation with serotonin (5-hydroxytryptamine), NaF, and guanosine $\text{5′-(3-O-}\text{thio}\text{)-}\text{triphosphate}$ (GTPγS) was time- and temperature-dependent. Mg²⁺ was required for enzyme activation. Adenylate cyclase that was activated by NaF or GTPγS was gradually inhibited by $\text{N-}\text{methylmaleimide}$ while enzyme activated with serotonin and GTP responded faster to inhibition by the same sulfhydryl reagent. The enzyme responded in a similar fashion to a spin-labeled $\text{N-}\text{methylmaleimide}$ analog 3-(maleimidomethyl)-2,2,5,5-tetramethyl-1-pyrolidinyloxyl (i.e., $\text{N-}\text{methylmaleimide}$ nitroxide). Binding of the spin label was enhanced following enzyme activation by serotonin, NaF, or GTPγS in the presence of Mg²⁺. Activation of the enzyme was accompanied by an increase in the strong immobilization peaks in the EPR spectra. Both effects, the increase in binding and in the strong immobilization peaks, can be induced by Mg²⁺ alone. The results indicate that a general conformational change induced by Mg²⁺ may be essential for adenylate cyclase activation.