ABSTRACT
The biological significance of the carbohydrate moiety of a glycoprotein has been a matter of much speculation. In the present work, we have chosen stem bromelain from Ananas comosus as a model to investigate the role of glycosylation of proteins. Stem bromelain is a thiol protease which contains a single hetero-oligosaccharide unit per molecule. Here, the deglycosylated form of the enzyme was obtained by periodate oxidation. The differences in the glycosylated and deglycosylated forms of the glycoprotein have been studied at various temperatures and pH values, using probes such as loss of enzyme activity and by the changes in fluorescence and circular dichroism spectra. Deglycosylated bromelain showed decreased enzyme activity and perturbed fluorescence and circular dichroism spectra. In addition to this, a comparative study of their activities in different organic solvents showed a marked decrease in case of deglycosylated form of the enzyme. It is thus concluded that glycosylation contributes towards the functional stability of glycoenzymes.
Subject(s)
Alcohols/pharmacology , Bromelains/metabolism , Circular Dichroism , Enzyme Stability , Glycosylation , Hydrogen-Ion Concentration , Spectrometry, Fluorescence , Substrate Specificity , TemperatureABSTRACT
La glucación no enzimática de casi todas las proteínas ocurre solamente en los grupos E-amino de los residuos de la lisina. Se estudió la hidrólisis catalizada por tripsina bovina, tripsina porcina y bromelina de piña, utilizando proteínas nativas y glucadas como substratos. La avoalbúmina, la albúmina humana, la T-globulina y la mioglobina glucadas, mostraron una reducida susceptibilidad ante la degradación por la tripsina, en comparación con las proteínas no glucadas, aparentemente por modificación directa de los residuos de lisina. La tripsina hidroliza a os substratos en las uniones peptídicas de las argininas y lisinas. La bromelina, una enzima menos específica, muestra velocidades similares en la hidrólisis para la caseína, avoalbúmina y mioglobina no glucadas y velocidades idénticas para la hemoglobina y la mioglobina glucadas. La tripsina bofina mostró un 100% de disminución en su actividad enzimática con albúmina humana y T-globulina glucadas y la bromelina con la albúmina humana glucada