Acid Amyloglucosidase and Carbohydrate Regulation

Abstract

High activity of the exoamylolytic enzyme, acid amyloglucosidase, was found in isolated pancreatic islets of the mouse. Enzyme activity was optimum at pH 5.0-5.5 and the activity at pH 5.0 was two times that of liver and ten times that of skeletal muscle. Acid amyloglucosidase activity in islets isolated from alloxan diabetic animals was reduced to about 10% of the normal value indicating that the major part of the enzyme activity is confined to islet β-cells. In contrast, islets isolated from insulin-hypersecreting obese mice (AO-mice) were found to have markedly elevated levels of acid amyloglucosidase activity.

Acid amyloglucosidase activity in islet homogenates prepared in osmotically protected media displayed both latency and sedimentability which together with its acid pH-optimum is suggestive of a lysosomal localization of the enzyme. It is hypothesized that lysosomes (through association with acid amyloglucosidase) may be involved in insulin secreting processes evoked by β-cell glycogenolysis.

Key words

Acid Amyloglucosidase Activity - Isolated Pancreatic Islets - Lysosomes - Alloxan Diabetes NMRI Mice - Obese Hyperglycemic Mice

1 The term acid amyloglucosidase is preferred to the generally used glucoamylase (E.C.3.2.1.3) or α-glucosidase (E.C. 3.2. 1.20) because it is considered a suitable descriptive term for the enzyme activity recorded in the present study. The term acid amyloglucosidase is not limited to an enzyme capable of splitting only a-l,4-bonds, nor does it cover other possible neutral glucoamylases or acid and neutral maltases not operating on glycogen at acid pH.

1 The term acid amyloglucosidase is preferred to the generally used glucoamylase (E.C.3.2.1.3) or α-glucosidase (E.C. 3.2. 1.20) because it is considered a suitable descriptive term for the enzyme activity recorded in the present study. The term acid amyloglucosidase is not limited to an enzyme capable of splitting only a-l,4-bonds, nor does it cover other possible neutral glucoamylases or acid and neutral maltases not operating on glycogen at acid pH.