Measurement of serum glycosylated proteins and glycosylated low density lipoprotein fraction in diabetes mellitus

A simple method was developed for estimating serum glycosylated protein levels using gel filtration with Bio-Gel P6 by determining the protein and sugar content in the void volume fraction. The glycosylated protein levels (GSP) correlated well with fasting blood sugar levels and glycosylated albumin level (G-ALB) determined by affinity chromatography with Blue Sepharose CL6B. The glycosylation level of heparin-citrate precipitable fraction of serum which predominantly contained low density lipoprotein (G-LDL) also correlated well with GSP and LDL-cholesterol levels. Significantly different values were obtained for GSP, G-ALB, and G-LDL between normals and diabetics.     

The transforming growth factor beta type II receptor can replace the activin type II receptor in inducing mesoderm.

The type II receptors for the polypeptide growth factors transforming growth factor beta (TGF-beta) and activin belong to a new family of predicted serine/threonine protein kinases. In Xenopus embryos, the biological effects of activin and TGF-beta 1 are strikingly different; activin induces a full range of mesodermal cell types in the animal cap assay, while TGF-beta 1 has no effects, presumably because of the lack of functional TGF-beta receptors. In order to assess the biological activities of exogenously added TGF-beta 1, RNA encoding the TGF-beta type II receptor was introduced into Xenopus embryos. In animal caps from these embryos, TGF-beta 1 and activin show similar potencies for induction of mesoderm-specific mRNAs, and both elicit the same types of mesodermal tissues. In addition, the response of animal caps to TGF-beta 1, as well as to activin, is blocked by a dominant inhibitory ras mutant, p21(Asn-17)Ha-ras. These results indicate that the activin and TGF-beta type II receptors can couple to similar signalling pathways and that the biological specificities of these growth factors lie in their different ligand-binding domains and in different competences of the responding cells.     

Correlation of phospholipid structure with functional effects on the nicotinic acetylcholine receptor. A modulatory role for phosphatidic acid.

Fourier transform infrared spectroscopy is used to characterize specific interactions between negatively charged lipids, such as phosphatidic acid, and the purified nicotinic acetylcholine receptor from Torpedo californica. The specific interaction of phosphatidic acid with acetylcholine receptor is demonstrated by the receptor-induced perturbation of the lipid ionization state, which is monitored using Fourier transform infrared bands arising from the phosphate head group. The acetylcholine receptor shifts the pKa of phosphatidic acid molecules adjacent to the receptor to a lower value by almost 2 pH units from 8.5 to 6.6. Decreased pH also leads to changes in ion channel function and to changes in the secondary structure of the acetylcholine receptor in membranes containing ionizable phospholipids. Phospholipase D restores functional activity of acetylcholine receptor reconstituted in an unfavorable environment containing phosphatidylcholine by generating phosphatidic acid. Lipids such as phosphatidic acid may serve as allosteric effectors for membrane protein function and the lipid-protein interface could be a site for activity-dependent changes that lead to modulation of synaptic efficacy.     

Isolation, Purification and Partial Characterisation of Urease from Seeds of Water Melon (Citrullus vulgaris)

Urease from seeds of water melon was purified to apparent homogeniety upto a sp act of 3750 units/mg protein with 31% recovery. Enzyme showed single protein band on native PAGE by urease specific staining. The mol wt of the enzyme was 4,70,000 and the preparation was free from bound nucleotides (A₂₈₀/A₂₆₀=1.14). The enzyme exhibited maximum activity in 50 mM Tris-acetate buffer (pH 8.5). The Km for urease was 8 mM. The enzyme was not inhibited by 25 mM of EDTA in 50 mM Tris-acetate buffer (pH 8.0 and 8.5).     

The proposed 5′-nucleotidase inhibitor in human leukemic cells is an artefact

It is now well established that human lymphoblastoid cell lines showing immaturity characters display ecto-5′-nucleotidase activities lower than normal levels. A recent paper (Sun, A.S., Holland, J.F. and Ohnuma, T. (1983) Biochim. Biophys. Acta 762, 577–584) mentioned that this phenomenon resulted from the presence of a 5′-nucleotidase inhibitor in these cell lines. We demonstrate here that the use of 5′-[³H]AMP as a substrate, and inadequate analysis of the products formed, led them to a misinterpretation. [³H]Adenosine derived from 5′-[³H]AMP hydrolysis was further transformed into [³H]inosine by the adenosine deaminase activity of the leukemic cell lines tested; [³H]inosine was precipitated with the excess substrate and was not taken into account in the ecto-5′-nucleotidase determination, which led the authors to confuse this adenosine deaminase activity with a 5′-nucleotidase inhibitor. We did not observe 5′-nucleotidase inhibition by leukemic cell cytosol when convenient assay methods were used and showed that the presence of such an inhibitor remains to be established.