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Physicochemical characteristics of insulin secretion granules.

ABSTRACT: beta-Granules were prepared from micro-dissected pancreatic islets of obese-hyperglycaemic mice. This fraction contained 60% of the insulin, 30% of the cytochrome oxidase, 16% of the acid phosphatase activity and 20% of the protein present in whole islets. The isolated granules retained a heavy metal during fractionation. Optimum conditions for granule stability were low ionic strength and pH6, the granules being unexpectedly fragile at pH7.4. The stability of the granules was unaffected by sucrose in the concentration range 50-320mm, but 1% (w/v) sodium deoxycholate released all insulin. A solubilizing effect was also noted with ATP and citrate. Spinning through 1.6m-sucrose yielded a further purification in relation to mitochondria and acid-phosphatase-carrying particles but virtually no purification in relation to protein. Electron microscopy revealed that the major contaminants were rough-surfaced vesicles and membranes. A separation of granules from acid phosphatase was achieved by phase distribution in polyethylene glycol and dextran. The location of the enzyme to the interphase was so pronounced in systems buffered with lithium phosphate that the technique may be used for future purification of acid-phosphatase-carrying particles from the beta-cells.

SUBMITTER: Coore HG

PROVIDER: S-EPMC1187500 | biostudies-other | 1969 Jan

REPOSITORIES: biostudies-other

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Project description:BackgroundThe increase in diabetes worldwide is alarming. Decreased acute insulin response to intravenous glucose tolerance test (IVGTT) during first-phase insulin secretion (FPIS) is a characteristic of diabetes. However, knowledge of the insulin secretion characteristics identified by different time to glucose peak in subjects with different metabolic state is sparse.AimsThis study aimed to find different patterns of FPIS in subjects with normal glucose tolerance (NGT) and analyzed the relationship between insulin secretion patterns and the risk for development of type 2 diabetes mellitus (T2DM).MethodsA total of 126 subjects were divided into three groups during a 10-min IVGTT, including NGT with time to glucose peak after 3 min (G1, n = 21), NGT with time to glucose peak at 3 min (G2, n = 95), and prediabetes or diabetes with time to glucose peak at 3 min (G3, n = 10). Glucose, insulin, and C-peptide concentrations at 0, 3, 5, 7, and 10 min during the IVGTT were tested. IVGTT-based indices were calculated to evaluate the insulin secretion and insulin sensitivity.ResultsAge, body mass index (BMI), waist-to-hip ratio, triglyceride (TG), and hemoglobin A1c (HbA1c) of subjects were gradually higher, while high-density lipoprotein cholesterol (HDL-C) was gradually lower from G1 to G3 (p for linear trend <0.05), and the differences between G1 and G2 were also statistically significant (p < 0.05). Glucose peak of most participants in G1 converged at 5 min, and the curves shape of insulin and C-peptide in G2 were the sharpest among three groups. There was no significant difference in all IVGTT-based indices between G1 and G2, but AUCIns, AUCIns/AUCGlu, and △Ins3/△Glu3 in G2 were the highest, and the p-value for linear trend of those indices among three groups were statistically significant (p < 0.05).ConclusionsTwo patterns of FPIS were in subjects with NGT, while subjects with later time to glucose peak during FPIS might be less likely to develop T2DM in the future.

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Physicochemical characteristics of insulin secretion granules.

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