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Biomedical subjects

F Melani

Publications and source records attributed to F Melani.

At least 55 records · Page 3Linked to original sources
PubMed1975

Chromatographic heterogeneity of insulin extracted from insulomas.

On gel filtration of acid-ethanol extracts from three pancreatic beta-cell adenomas 1.4% to 1.8% of total immunomeasurable insulin (IMI) eluted ahead of proinsulin. This high molecular IMI was resolved into three components. The presence of urea in the dilute acetic acid solutions of extracted tumor tissue did not influence the pattern of gel filtration. High molecular IMI dissolved in dilute acetic acid showed to be stable if immediately rechromatographed, but a partial dissociation to insulinlike and proinsulinlike components (ILC and PLC) was found if rechromatography was performed after 48 h of incubation. Mainly ILC and PLC were found on rechromatography provided high molecular IMI was dissolved and incubated briefly in 0.04M phosphate buffer, pH 7.4. It proved improbable that the proteolytic action of some protein being extracted with the hormones caused a splitting of high molecular IMI at pH 7.4. We conclude from our findings that the components of high molecular IMI are not precursors of proinsulin and insulin but are either self-associated products of the hormones or associations of insulin and proinsulin to other proteins extracted from insuloma tissue.

Adenoma, Islet Cell↗
PubMed1971

Molecular aspects of the regulation of rat kidney alkaline phosphatase.

The mechanisms by which phosphate regulates the activity of alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) in rat kidney were investigated. Measurements of incorporation of [(14)C]leucine into kidney alkaline phosphatase in rats fed on complete or phosphate-free diet provide evidence of a twofold increase in the rate of synthesis of the enzyme in diet-treated animals. Cycloheximide experiments indicated that control and diet-adapted enzyme decreases in activity according to first-order kinetics with a calculated half-life of 10.3 and 6.5h after complete and phosphate-free diet administration respectively. Basal and diet-adapted enzymes exhibit similar K(m) values for several phosphomonoesters and an identical degree of inhibition is produced by cysteine. In addition, the enzyme from both sources is the same with regard to heat inactivation at 45, 56 or 64 degrees C, to the profile of elution from Sephadex and to electrophoretic properties on polyacrylamide gel. A failure of rat kidney alkaline phosphatase to respond to cortisol (hydrocortisone) was also observed.

Adrenal Glands↗
PubMed1970

Identification of proinsulin and C-peptide in human serum by a specific immunoassay.

An immunoassay for the measurement of human proinsulin and C-peptide is described. By a combination of this system and an insulin immunoassay, proinsulin, insulin, and C-peptide were identified in acid-ethanol extracts of serum after gel filtration. In keeping with the results of biosynthetic studies, insulin and C-peptide were found to be present in equimolar amounts. The absolute values of serum proinsulin determined independently in the two assays corresponded closely.

Adenoma, Islet Cell↗
PubMed1970

Human serum proinsulin.

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-(131)I 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.

Adolescent↗