Involvement of glycoconjugates in insulin-receptor interactions. Studies in liver plasma membranes of control and diabetic mice

The involvement of glycoconjugates in the insulin-receptor interactions in mouse liver is tested by digestions of membranes with various enzymes. Trypsin decreased the binding of [125I]insulin to liver membranes. After digestion with beta-galactosidase no ""high affinity'' receptor sites could be detected. The effects observed with plant lectins confirm the involvement of galactoconjugates in the insulin binding process. Sophora japonica and Ricinus communis lectins (with galactose specificity) and concanavalin A largely inhibit the binding process of insulin and those effects concern the ""high affinity'' receptor sites. Other lectins (wheat germ agglutinin, Dolichos) and enzymes (alpha-L-fucosidase, beta-N-acetyl-hexosaminidase and neuraminidase) are without effect on insulin binding. Comparative studies performed on diabetic mouse liver membrane (KK mice), previously characterized by decreased number of insulin receptors, are in good agreement with qualitatively similar receptor sites in both non-diabetic (control) and diabetic mice. Effects of enzymes and lectins yielded same results as compared to control membranes. Plasma membrane proteins and glycoproteins in both types of mouse are indistinguishable with respect to enzymic and chemical analysis. Sodium dodecyl sulphate acrylamide gel electrophoresis shows identical patterns. Moreover, the decrease in the number of insulin receptors is easily reversed with diet restriction. These data are consistent with the similarity of receptor sites in control and diabetic liver membrane.

N-Terminal amino acid sequence of rat tonin: homology with serine proteases

In this paper, we present the amino-terminal sequence of rat tonin, an endopeptidase responsible for the conversion of angiotensinogen, the tetradecapeptide renin substrate, or angiotensin I to angiotensin II. It is shown that isoleucine and proline occupy the amino- and carboxy-terminal residues respectively. The N-terminal sequence analysis permitted the identification of 34 out of the first 40 residues of the single polypeptide chain composed of 272 amino acids. These results showed an extensive homology with the sequence of many serine proteases of the trypsin-chymotrypsin family. This information, coupled with the slow inhibition of tonin by diisopropylfluorophosphate, classified this enzyme as a selective endopeptidase of the active serine protease family.

[Detection of antigenic determinants of membranes using an insoluble peanut lectin]

The binding of lectins on insoluble supports may be used to detect the interactions occurring between these molecules and the sites of some receptors of membranes. An example is given, using the "anti-T" lectin extracted from peanut, to show the presence of determinants with terminal free glactose on the surface of erythrocytes and lymphocytes.

Application of affinity electrophoresis to the study of antigen-immunoadsorbent association equilibrium

Affinity electrophoresis is used to study the interaction of complementary biological molecules. Using Scatchard plots, this method gives a partition ratio between immunoadsorbent and soluble antigen or antibody. In the present work, affinity electrophoresis, used to study the interaction between human serum albumin and its insolubilized antibodies, allows a measure of the system's affinity under specific conditions, in particular, the electric field.

[Example of the use of affinity electrophoresis for the determiniation of antigens]

In this paper, affinity electrophoresis is employed to obtain a quantitative evaluation of an antigen using biospecific immunoadsorbant. As an example it is shown that human serum albumin reacts with its specific antibodies linked to agarose beads forming "rockets" in the gel. The height of these "rockets" corresponds to the quantity of albumin in the medium. This method assumes the immobilization of the antibodies in the gel with all the buffers employed.

Evidence for a conformational change in tRNAPhe upon aminoacylation

A conformational difference between the structure of tRNAPhe and Cbz-Phe-tRNAPhe from Escherichia coli was detected using the spin label method. A comparison of the respective rotational correlation time (tau c) values of three differently located spin labels, indicates that upon aminoacylation of tRNAPhe, the 4-thiouridine residue region and the miniloop region become more flexible, while the environment of the anticodon loop is not affected. These observations suggest that the main difference in structure between charged and uncharged tRNA resides in the release and exposure of the TpsiC loop for eventual binding to the ribosomes.

A spin label study of the thermal unfolding of secondary and tertiary structure in E. colic transfer RNAs

The molecular mechanism of thermal unfolding of E. coli tRNAGlu, tRNAfMet and tRNAPhe (in 0.02M Tris-HC1, pH 7.5. 10 MM Mg C12) has been examined by the spin-labeling technique. The rate of tumbling of the spin label has been measured as a function of temperature for ten different selectively spin-labeled tRNAs. Only spin labels at position s4U-8 were able to probe the tertiary structure. Evidences are presented which support the hypothesis that the thermal denaturation of the three species of tRNAs studied is sequential. The unfolding process occurs in three discrete stages. The first step (30 degrees-32 degrees) could either be assigned to a localized reorganization of the cold-denatured structure or to a "transient" melting, followed by the simultaneous disruption of the tertiary structure and part of the hU helix. This transition is observed even in the absence of magnesium. The second step (50 degrees-54 degrees) involves the melting of the anticodon and miniloop regions. The last step occurs above 65 degrees where the t psi c and amino acid acceptor stems, forming one continuous double helix, melt. A simple dynamic model is considered for tRNA function in protein biosynthesis.

Specific spin-labeling of transfer ribonucleic acid molecules

The spin labels anhydride (ASL), bromoacetamide (BSL) and carbodiimide (CSL) were used to label selectively tRNAGlu, tRNA fMet and tRNAPhe from E. coli. The preparation and characterization of the sites of labeling of eight new spin-labeled tRNAs are described. The sites of labeling are: s2U using ASL, BSL and CLS and tRNAGlu; s4U using ASL and BSL on tRNAfMet and tRNAPhe; U-37 with CSL on tRNfMet; U-33 with CSL on tRNAPhe. The rare base X at position 47 of tRNAPhe has been acylated with a spin-labeled N-hydroxysuccinimide (HSL). The 3'end of unfractionated tRNA molecules has been chemically modified to a morpholino spin-labeled analogue (MSL). Their respective e.s.r. spectra are reported and discussed.

Decreased binding of insulin to liver plasma membrane receptors in hereditary diabetic mice

The interaction of insulin with its receptors was studied in liver plasma membranes of the young non-obese hereditary diabetic mouse (KK strain). Under identical conditions of preparation and incubation, the membranes of the KK mouse bind only 55-70% as much insulin per mg of protein as those of the control mouse (Swiss albino). Scatchard analysis suggests that this decrease in binding is due to a decrease in the number of receptor sites in the membrane of the diabetic mouse. However, the membranes of diabetic and control mice do not exhibit significant differences in hexosamine and sialic acid contents, enzyme activities, and protein and glycoprotein analysis. The decrease in insulin receptors in the KK mouse seems to correlate with the insulin resistance which they exhibit.

Practical concepts of drug absorption, distribution and loss

Serum concentrations of ampicillin were measured following administration of the drug orally and intravenously to nine normal volunteers. The results were analysed by graphic methods, and the effects of absorption, distribution and loss on the time serum concentration curve are discussed.

Comparative bioavailability of three brands of ampicillin

The relative biological availability (bioavailability) of three brands of ampicillin trihydrate capsules marketed in Canada was studied by means of a crossover experimental design and was evaluated by analysis of variance. After administration of a single oral dose (500 mg.) to volunteer subjects, the mean peak ampicillin serum concentration and the area under the time ampicillin serum concentration curve (AUC) were higher for one of the products than for the other two. A second study utilizing the same experimental design revealed no differences in these parameters when different production lots of the more available product were compared. Product bioavailability was not related to the in vitro dissolution time of the capsules. The experimental design and methods of statistical analysis are discussed.