Periodate oxidation of carbohydrate moiety of stem bromelain without much alteration in enzymatic activity

Additional stabilization of stem bromelain coupled to a thermosensitive polymer by uniform orientation and using polyclonal antibodies

Stem bromelain was covalently coupled to a thermosensitive polymer of N-isopropylacrylamide (p(NIPAm)) either through the amino groups of the enzyme (randomly coupled) or via the lone oligosaccharide chain (uniformly coupled). The enzyme coupled via the oligosaccharide chain exhibited better access to the substrate casein as compared to the preparation in which the amino groups formed the point of contact between the enzyme and the polymer. Native bromelain exhibited a pH optimum of 8.0 and a broad pH-activity profile. The polymer-coupled preparations exhibited broader pH-activity profiles and shifting of pH optimum to 10.0 at 35 degrees C. At 25 degrees C, the shifting of pH optimum was observed for the randomly coupled enzyme only. The temperature-activity profiles of bromelain coupled to p(NIPAm) also showed appreciable broadening and the preparations retained greater fraction of maximum activity above the temperature optimum. The optimum temperature of the uniformly oriented preparation also rose to 70 degrees C. Inactivation rates of the polymer-coupled bromelain were remarkably low at 60 degrees C as compared to the native protease, and binding of antibromelain antibodies improved the resistance to inactivation of the polymer-coupled preparations. The cleavage patterns of hemoglobin and IgG by the native bromelain and the polymer-coupled preparations were comparable.

1-Deoxyglycitolation of protein amino groups and their regeneration by periodate oxidation

Reductive alkylation of lysyl epsilon-amino groups with sugars (1-deoxyglycitolation) using pyridine borane as the reducing agent has been recently described [Wong, W.S.D., Osuga, D.T. & Feeney, R.E. (1984) Anal. Biochem. 139, 58-67]. The regeneration of the lysines has now been achieved by oxidation with approximately 10 mM periodate. In experiments with glycitolated bovine serum albumin, reactions using 5, 20, and 80 mM periodate were essentially complete in the first 10 min. Oxidations of methionine to the sulfoxide were evident even at this lower concentration of periodate, while higher concentrations and prolonged reaction times only caused unnecessary destruction of amino acids. The removal was shown to occur in a wide pH range with little variation in the recovery of the lysines. The degree of glycitolation, or the nature of the attached carbohydrate residues, had no effect on the yield of products. Reductive 1-deoxygalactitolation of approximately 55% of the lysyl epsilon-amino groups of lysozyme caused no loss in enzymatic activity; when 5 mM periodate was used to remove the 1-deoxygalactitol moiety, approximately 95% of the amino groups were regenerated, concomitant with destruction of approximately 16% of the activity. On reductive 1-deoxygalactitolation of the amino groups of turkey ovomucoid, 65% of the lysyl epsilon-amino groups were modified with 70% loss of the inhibitory activity against trypsin. On treatment with 5 mM periodate, approximately 80% of the amino groups were regained with a similar recovery of the inhibitory activity.

Isolation and characterization of Taka-amylase A apoprotein deglycosylated by digestion with almond glycopeptidase immobilized on Sepharose

Taka-amylase A (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1), which contains a single asparagine-linked oligosaccharide unit, was digested with almond glycopeptidase immobilized on Sepharose 6B at 20 degrees C for 4 h. A maximum of 10% of the parent protein was isolated as apoprotein by column chromatography on Con-A Sepharose. The characteristics of the apoprotein were compared to those of the native Taka-amylase A. The removal of the sugar chain from Taka-amylase. A caused no change in the pH-activity profile or in kinetic parameters of the hydrolysis of soluble starch. The stability of the apoprotein toward changing pH and digestion by proteases did not show any appreciable difference from that of the native Taka-amylase. These results suggest that the carbohydrate moiety of Taka-amylase A is not an essential participant in the catalysis.

Structural studies on periodate-oxidized chicken ovomucoid. Spectral behaviour of the tyrosine residues

About 50% of the carbohydrate moiety of ovomucoid was destroyed by periodate oxidation. The oxidation was carried out for 6 h or 24 h. The data obtained showed that in the carbohydrate chain 2-5 glucosamines and 1-2 neutral sugar residues were decomposed with the consumption of 16 mol and 29 mol of periodate respectively. Periodic oxidation slightly changed the inhibitory activity of the ovomucoid, but altered its spectral properties. An increase of the absorption maximum at 278 nm was noted, as well as a tendency for normalization of phenolic ionization and an increase of the relative fluorescence. The reactivity of tyrosine residues towards tetranitromethane is also changed. It was suggested that even in native ovomucoid the tyrosines could be regarded as 'dissolved' in the 'carbohydrate solvent'. This contact could be achieved by the hydrogen bonds in the formation of which the NHCOCH3 groups of the glucosamine residues play an essential role. Peroxidate oxidation seems to lead to an alteration of the nature of the 'sugar solvent' and disturbs the conformation of the sugar chain.

Effect of periodate oxidation on the structure and properties of glucose oxidase

In order to elucidate the molecular structure of glucose oxidase (beta-D-glucose: oxygen 1-oxidoreductase, EC 1.1.3.4) and the roles of its carbohydrate moiety, chemical, physiochemical and immunological experiments were performed with enzyme samples before and after periodate oxidation. Hydrodynamic parameters indicated that the native enzyme was a globular protein with values of 1.21 for the frictional ratio and 43 A for the Stokes radius. The enzyme contained about 12% carbohydrate by weight, of which the main component was mannose. The periodate treatment decreased the carbohydrate content to about 40% of its original value. Slight modifications were detected in the absorbance spectrum and the content of arginyl residue. However, no significant alteration was brought about by this treatment in the catalytic parameters, immunological reactivities of the gross structure, not in the secondary and quaternary structures of the protein moity. Thermal denaturation temperature (about 72.5 degrees C) and the enthalpy of denaturation (about 450 kcal/mol) were common to the native and the periodate-oxodozed enzymes. The native was found to be quite resistant to sodium dodecyl sulfate and fairly stable to urea and heating. The periodate-oxidized enzyme was also stable to heat treatment, but it showed a diminished stability when denaturing agents were present. Kinetic analyses of the thermal inactivation processes showed that the entropy of activation was greatly decreased by the denaturing agents, especially in the case of the periodate-oxidized enzyme. It is concluded that the carbohydrate moiety of the enzyme plays a role in increasing the stability of the protein moiety, but does not directly participate in the catalytic activity, the immunological reactivity, or in maintaining the conformation of the enzyme protein.

Photosensitized inactivation of stem bromelain. Oxidation of histidine, methionine, and tryptophan residues

Pineapple stem bromelain was photooxidized in the presence of Methylene Blue used as a sensitizer. The essential sulfhydryl group of the enzyme protein rapidly became inaccessible to react with 5,5'-dithiobis(nitrobenzoic acid), but the reactivity was readily regained to the original level upon treatment with dithiothreitol. Even after such reduction, the photooxidized enzyme showed a markedly decreased hydrolytic activity on casein. Spectral examination revealed that the oxidized enzyme had tyrosine residues intact. Amino acid analysis showed significant decreases in histidine, ethionine, and tryptophan residues. Photoinactivation occurred in a similar manner also in the presence of tetrathionate which reversibly blocked the essential sulfhydryl group. It is concluded that the irreversible photoinactivation of stem bromelain must be related to the oxidation of histidine, methionine, and tryptophan residues. When the photooxidation was carried out a different pH values ranging from 4.0 to 8.3, the inactivation and the decrease in histidine content were found to be markedly pH dependent. Thus, the photooxidation experiment provided a method for directly measuring the apparent pKa of the ionization of the single histidine residue in stem bromelain. Apparent pKa values of 6.4 and 7.1 were obtained for the histidine imidazole in the absence and in presence of tetrathionate, respectively. In view of these normal pKa values for an imidazole, a mechanism of ionization of the active-site group in a plant thiol proteinase is proposed, in which the validity of mechanism involving a close electronic interaction between histidine and cysteine residues is seriously questioned.