Selectivity of the insulin-like actions of vanadate on glucose and protein metabolism in skeletal muscle.

The 1H-n.m.r. spectrum of casein micelles consists of a small number of moderately sharp (linewidth approx. 60 Hz) resonances superimposed on the envelope of very broad lines expected for particles of this size. These sharp lines resemble, in chemical shift and relative intensity, the spectrum of the isolated 'macropeptide' released from the micelles by treatment with chymosin. The sharp lines in the casein micelle spectrum are further sharpened by addition of chymosin and broadened markedly by addition of ethanol. These observations are consistent with the proposal that the 'macropeptide' (the C-terminal 64 residues of K-casein) forms flexible 'hairs' on the surface of the micelles.     

Histamine H2 receptors on chondrocytes derived from human, canine and bovine articular cartilage.

Histamine (1-100 microM) induced a concentration-dependent increase in intracellular cyclic AMP in monolayer cultures of human, canine and foetal-bovine articular chondrocytes. The dose-response curve for histamine in each culture was progressively displaced to the right with increasing concentrations of cimetidine, an H2-receptor antagonist. The histamine-induced cyclic AMP elevation in human articular chondrocytes was also significantly decreased by ranitidine, another H2 antagonist, but not by the H1 antagonists mepyramine and chlorpheniramine. These findings indicate that histamine activates chondrocyte adenylate cyclase through an H2 receptor. The cyclic AMP response of human chondrocytes to histamine was many times greater than that measured for synovial fibroblasts under similar conditions. Such findings suggest that mast-cell-chondrocyte interactions in vivo may contribute to changed chondrocyte metabolism in joint disease.     

The sporulation-specific penicillin-binding protein 5a from Bacillus subtilis is a DD-carboxypeptidase in vitro

A chemiluminescence method for determining acetylcholinesterase activity is described. It is an adaptation of the chemiluminescence assay of acetylcholine described by Israël & Lesbats [(1981) Neurochem. Int. 3, 81-90; (1981) J. Neurochem. 37, 1475-1483]. The acetylcholinesterase activity is measured by monitoring the increase in light emission produced by the accumulation of choline or by determining the amount of choline generated after a short interval. The assay is rapid and sensitive, and uses the natural substrate of the enzyme. Kinetic data obtained with this procedure for acetylcholinesterase from Torpedo and Electrophorus electric organs were comparable with those obtained by using the method of Ellman, Courtney, Andres & Featherstone [(1961) Biochem. Pharmacol. 7, 88-95]. In addition, it was shown that sodium deoxycholate totally inactivated Torpedo acetylcholinesterase but not the Electrophorus enzyme. Competitive inhibitors of acetylcholinesterase protected the enzyme from inactivation.     

Effect of vitamin B-6 (pyridoxine) deficiency on lung elastin cross-linking in perinatal and weanling rat pups.

Weanling and perinatal rats were rendered vitamin B-6 (pyridoxine)-deficient. The rat pups were nursed from vitamin B-6-deficient or -sufficient dams and were killed at day 15 after parturition. The weanling rats were fed vitamin B-6-deficient or -sufficient diets and were killed after 5 weeks of treatment. Lung elastin from the groups of rats was then studied with respect to its content of lysine-derived cross-linking amino acids. Lung lysyl oxidase activity was also measured. B-6 deficiency decreased the number of lysine residues in elastin that were converted into the cross-linking amino acid precursor allysine. However, a more significant defect in cross-link formation was an apparent block in the condensation steps leading to the formation of desmosine. Desmosine was decreased, with an increase in the amounts of aldol condensation products (aldol CP) in elastin. It is proposed that the elevation in aldol CP results from the formation of thiazines, which are produced from the reaction between aldehyde and homocysteine. The concentration of homocysteine is significantly elevated in vitamin B-6-deficient rats.     

The thiol groups of mouse immunoglobulin A. Incomplete formation of the C alpha 1-domain disulphide bridge.

The BALB/c IgA (immunoglobulin A) myeloma protein M167 contained on average 5.7 free SH groups per IgA dimer. These groups were preponderantly on the heavy chains and comprised two distinct populations: 3.3 exposed SH groups per dimer in the Fc region, and 2.4 buried SH groups per dimer in the Fd region, detectable o only after denaturation. To locate the cysteine residues involved, labelled peptides were purified from thermolysin digests of radioalkylated IgA by high-performance liquid chromatography. From the amino acid compositions of the peptides, the exposed thiol groups were assigned to Cys-307 in the C alpha 2 domain, which thus existed in the reduced form to an extent exceeding 80%. This residue may allow attachment of secretory component to dimer IgA in the mouse to proceed via thiol-disulphide exchange. The buried thiol groups were assigned to Cys-150 and Cys-208, in the C alpha 1 domain, each being in the reduced form to the extent of approx. 30%. This pair of residues would normally give rise to the characteristic intradomain disulphide bridge. It appears that disulphide formation is not a crucial event during folding of the C alpha 1 domain in IgA biosynthesis. The sequence in the region 140-151 was re-investigated, and residue 142 was shown to be serine, not cysteine, helping explain the lack of heavy-chain-light chain bonding in BALB/c mouse IgA. A disulphide-bond model for mouse IgA is proposed on the basis of these assignments and other features of the mouse alpha-chain sequence.     

Comparison of the structure of two cardiac troponin T isoforms.

Two isoforms of troponin T have been isolated from bovine cardiac muscle. One isoform has an Mr of 31000 and a pI at about 7.1, the corresponding values for the second isoform being 33000 and 6.5. Both isoforms have identical C- and N-terminal sequences, and, according to the data from tryptic-peptide mapping, a similar structure of the central and C-terminal domains. The large N-terminal peptides of troponin T isoforms differ in the content of glutamine/glutamic acid and alanine. It is concluded that the isoform with Mr 33000 has an additional peptide enriched with glutamic acid and alanine that is inserted between the N-terminal pentapeptide and the cysteine located 40-60 residues from the N-terminus.     

N2-(1-carboxyethyl)methionine. A ''pseudo-opine'' in octopine-type crown-gall tumours.

A novel methionine-containing plasmid-determined compound, N2-(1-carboxyethyl)methionine (NCEM) has been identified in crown-gall tumours induced by octopine-type strains of Agrobacterium tumefaciens. NCEM is probably synthesized by octopine synthase. Cell-free preparations from octopine-type strains of A. tumefaciens can degrade NCEM; however, the bacterium cannot transport the compound into the cell, although these strains can take up and degrade the octopine family of opines.     

Human glyceraldehyde-3-phosphate dehydrogenase: mRNA levels and enzyme activity in developing muscle.

Analysis of human glyceraldehyde-3-phosphate dehydrogenase mRNA revealed that levels in adult skeletal muscle are 12-fold greater per microgram of polyadenylated RNA than in fetal skeletal muscle, whereas in cardiac muscle RNA levels were about equal in fetal and adult tissue. The mRNA levels correlate well with glyceraldehyde 3-phosphate dehydrogenase enzyme activities. There was no evidence for fetus- or tissue-specific forms.