RESUMO
Amphipathic enzymes, invertase (EC 3.2.1.26), 8-amylase (EC 3.2.1.3), and alkaline phosphatase (EC 3.1.3.1), were purified from the rat small intestinal mucosa as trypsin and Triton forms, the catalytic and regulatory characteristics of which were compared in rats and in drosophila. Differences in the catalytic propertiis of the two enzyme forms were demonstrated, which suggested that the hydrophobic part of the enzyme was involved in maintaining optimal conformation of the catalytic part. Many modifiers have beenfound to influence the Triton rather than the trypsin form of the enzyme. It is therefore suggested that the hydrophobic sub-units of the enzymes might be involved in transmitting information from the cytoplasm into the external surface of the membrane, the cell in this way regulating the activity of surface enzymes. If this is indeed the case, it is suggested that the hydrophobic part performs functions not only of external but also of internal regulation.
Assuntos
Membrana Celular/enzimologia , Hidrolases/metabolismo , Microvilosidades/enzimologia , Fosfatase Alcalina/metabolismo , Amilases/metabolismo , Animais , Catálise , Drosophila melanogaster , Concentração de Íons de Hidrogênio , Mucosa Intestinal/enzimologia , Mucosa Intestinal/ultraestrutura , Cinética , Polietilenoglicóis , Ratos , Sacarase/metabolismo , TripsinaAssuntos
Mucosa Intestinal/enzimologia , Intestino Delgado/enzimologia , Fosfatase Alcalina/análise , Animais , Dipeptidases/análise , Mucosa Intestinal/citologia , Masculino , Microvilosidades/enzimologia , Microvilosidades/ultraestrutura , Peptídeo Hidrolases/análise , Ratos , Especificidade por Substrato , alfa-Amilases/análiseRESUMO
The possible relative importance of the membrane and intracellular peptidases of the enterocytes in splitting dietary peptides to amino acids has been analysed. On the anoxic criterion, membrane hydrolysis was found to be predominant. Model experiments revealed cooperative interactions between the membrane enzyme and the coupled transport system. This cooperativity allows the main characteristics of oligomer transport to be described in terms of membrane digestion. Comparison of the behaviour of membrane and intracellular peptidase under different conditions has shown that the former are largely involved in digestion and the latter in intracellular metabolism. It is suggested that the efficiency of the membrane system is high enough to account for the hydrolysis of protein, especially taking into account the stimulation of enzyme processes in the brush border that occurs after ingestion of protein and carbohydrate. A sequential model based on the concept of three interacting enzyme layers (glycocalyx, lipoprotein membrane and cytosol) is presented.