Human serum proinsulin.
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It is concluded that the earlier eluting fraction of human serum extracts is proinsulin, as the relative proportions of the two hormones were in the same range observed in the normal group.Abstract:
Gel filtration of human serum extracts on Bio-Gel P-30 columns produced two peaks of material reactive with insulin antisera. The earlier eluting fraction appeared at the elution position of proinsulin (serum proinsulin-like component, PLC) while the second fraction corresponded in elution volume to insulin. In assays using porcine insulin-131I and an antiserum against porcine insulin, human pancreatic proinsulin was less reactive than human insulin. Serial dilutions of the serum PLC in the immunoassay showed immunological identity with the human proinsulin standard. Partial tryptic digestion of the serum PLC yielded products with increased immunological reactivity as estimated with insulin as the standard. With larger amounts of trypsin, all the serum PLC was converted to insulin-like components (desthreonine and desoctapeptide insulin). On the basis of these results we conclude that the earlier eluting fraction of human serum extracts is proinsulin.
The fasting values of proinsulin in normal subjects ranged between 0.05 and 0.4 ng/ml, representing from 5 to 48% of the insulin concentration. In one subject the values of proinsulin were higher than those of insulin. After oral administration of 100 g of glucose, the proinsulin levels tended to rise similarly to insulin. Three obese patients with hyperinsulinemia had higher fasting levels of proinsulin and a greater increase after glucose than the normal subjects. As the high levels of proinsulin coexisted with raised insulin concentration in these obese subjects, the relative proportions of the two hormones were in the same range observed in the normal group. Thus hyperinsulinemia in these obese subjects was not accompanied by an increase in the fraction of serum proinsulin. When the values for serum proinsulin were expressed as percentage of the insulin levels, there was a decrease in the per cent proinsulin in the first hour of the glucose tolerance test. After the second hour, the per cent tended to rise towards the fasting levels.read more
Citations
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Proinsulin, insulin, and C-peptide concentrations in human portal and peripheral blood.
TL;DR: The results indicate that under the conditions studied, insulin and C-peptide aresecreted in equimolar concentrations in man, and that proinsulin is secreted in the same proportion to insulin as found in the pancreas.
Journal ArticleDOI
A threshold distribution hypothesis for packet storage of insulin and its mathematical modeling
TL;DR: This hypothesis proposes that labile insulin is not stored in a homogeneous form but as packets with a bell-shaped distribution of thresholds to glucose that respond quickly when their threshold levels to glucose are reached or exceeded.
Journal ArticleDOI
Metabolism of Proinsulin, Insulin, and C-Peptide in the Rat
TL;DR: The renal handling of proinsulin, insulin, and C-peptide in the rat is defined and it is indicated that in this species the kidney represents a major site for insulin metabolism and is the main organ responsible for the degradation ofproinsulin andC- peptide.
Journal ArticleDOI
Serum proinsulin levels at fasting and after oral glucose load in patients with type 2 (non-insulin-dependent) diabetes mellitus
TL;DR: It is suggested that B cells may release ‘immature’ granules richer in proinsulin content as well as mature granules in the over-stimulated state in subjects with impaired glucose tolerance and diabetic patients.
Journal ArticleDOI
The Metabolism of Proinsulin and Insulin by the Liver
TL;DR: Significant differences in the capacity of the liver to remove and degrade insulin and proinsulin are indicated, which may account for its prolonged half-life in vivo and contribute to its relatively high plasma concentration in the fasting state.
References
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Journal ArticleDOI
The preparation of 131i-labelled human growth hormone of high specific radioactivity
TL;DR: The loss of immunological reactivity at high specific radioactivities or at high levels of chemical substitution with STAI/sup 127/!iodine is demonstrated.
Book
Methods of Biochemical Analysis
TL;DR: The Radiation Inactivation Method as a Tool to Study Structure-Function Relationships in Proteins Immunoassay with Electrochemical Detection and Theory and Newer Technology Assays for Superoxide Dismutase are studied.
Journal ArticleDOI
Immunoassay of Insulin: Two Antibody System: Plasma Insulin Levels of Normal, Subdiabetic and Diabetic Rats
Carl R Morgan,Arnold Lazarow +1 more
TL;DR: A two antibody system of insulin assay for immunoassay of insulin induces the production of specific nonprecipitating antibodies, both in experimental animals and in humans.
Journal ArticleDOI
A rapid photoelectric method for the determination of glucose in blood and urine
TL;DR: The present author has been able to obviate the difficulties of the Hawkins and Van Slyke method and yet retain the principle involved, and the resulting method is simple, easy, and accurate.
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