Syntheses of C-peptides and Human Proinsulin

Abstract

Syntheses of human, dog, rat, and duck C-peptides and their analogues and preliminary results on the total synthesis of human proinsulin are described. In the syntheses of the C-peptides, chain elongation was performed exclusively by the azide-fragment condensation method in solution. The synthetic human, dog, rat, and duck C-peptides and their analogues were proved to be homogeneous by several analytic means. With these synthetic peptides, radioimmunoassay systems for dog, rat, and duck C-peptides were developed. For the total synthesis of human proinsulin, 10 protected peptide hydrazides were prepared, and the linearly protected hexaoctacontapeptide having the proposed sequence of human proinsulin was constructed by the azide-fragment condensation method in solution starting from the C-terminal undecapeptide (HP 75-86). After deblocking of the alpha-amino protection, the partially protected hexaoctacontapeptide was treated with sodium in liquid ammonia. The ensuing sulfhydryl form was converted to the S-sulfonate form, which was reduced and then air-oxidized. The oxidized material was purified by gel filtration on Sephadex G-50 (fine) followed by ion-exchange chromatography on DEAE-cellulose. The cross-reactivity in the insulin radioimmunoassay of the ensuing product was 62.5 per cent of porcine proinsulin on a weight basis at B/Bo = 60 per cent. Acid hydrolysis and amino acid analysis of this product gave the theoretically expected ratios. In addition, this peptide, as well as the S-sulfonate form of the hexaoctacontapeptide, showed displacement curves superimposable on that of synthetic human C-peptide on an equimolar basis in the human C-peptide radioimmunoassay (antiserum 527). These results confirm the synthesis of human proinsulin.

C-Peptide Levels in Amniotic Fluid in Experimental Fetal Growth Retardation

“…Therefore C-pcptide is excreted in urine at a higher rate than insulin, and fetal insulin secretion is better reflected by the C-peptide in amniotic fluid than by insulin. When amniotic fluid samples are stored at -20 °C for 12-16 weeks, no fall of C-peptide reactivity is expected [8], The anti serum R 901 reacts with both rat C-peptide I and II and permits a mean recovery of 118% of 1/1 mixtures of synthetic rat C-pcptide I and II in doses ranging from 80 pg/tube to 10 ng/tube [7], A significantly lower mean C-peptide con centration in the amniotic fluid was found in the growth-retarded fetuses than in the con trols, and there was a highly significant posi tive correlation between C-pcptide levels in the amniotic fluid and the fetal body weights. These results confirm, in an experimental animal, the findings of Lin et al [9]: they found reduced C-peptide levels in the am niotic fluid in small for gestational age in fants in comparison with the C-peptide con centrations in appropriate for gestational age infants.…”

“…The antiserum used was R 901 raised in a rabbit immunized with PVP-adsorbed rat C-peptide II [7], The major antigenic site of antiserum R 901 is located within the C-terminal 52-63 se quence that has an identical structure in rat C-peptidc I and II. Therefore R 901 has similar reactivities with both rat C-peptides and measures the total of C-pep tide I and C-peptide II [7]. The standard and the anti serum were provided by A'.…”

Diurnal Variation of Blood Ketone Bodies in Insulin-Dependent Diabetes mellitus and Noninsulin-Dependent Diabetes mellitus Patients: The Relationship to Serum C-Peptide Immunoreactivity and Free Insulin

“…The intra-and interassay coefficients of variation (CV1, CV2) in TK were 2.7 and 2.5%, respectively, and those in AcAc were 4.3 and 2.5%. Glucose (CV1 2.5%, CV2: 2.0%) was measured by a glucose oxidase method [9], and FFA (CV1: 1.5%, CV2: 1.5%) by a previously described method [10], Insulin [11][12][13][14] (CV1: 5.6%, CV2: 5.4%), glucagon [15] (CV1: 5.3%, CV2: 3.6%) and S-CPR [16,17] (CV1: 2.8%. CV2: 3.5%) were assayed by kits purchased from Daiichi Radioisotope Labs.…”

Synthesis of potent antagonists of substance P by modifying the methionyl and glutaminyl residues of its C‐terminal hexapeptide and without using d‐amino acids

“…It has been shown from structure-activity studies that Met" residue of substance P (SP) is essential for activity and/or efficacy of S P (1). The role of the side chain of Met" and its a-carboxamide are rather associated with affinity of SP (2)(3)(4).…”