Vascular smooth muscle mitochondria: Magnesium content and transport

Endogenous magnesium content and magnesium transport of isolated bovine vascular smooth muscle mitochondria were studied. Mitochondria isolated from atherosclerotic bovine arteries contained two to three times as much magnesium (178 nmol/mg of mitochondrial protein) as those isolated from normal arteries (67 nmol/mg of mitochondrial protein). Electron-opaque granules were visible in the unstained unfixed mitochondria and could be shown with electron probe analysis to consist of magnesium, calcium, and phosphorus. At concentrations of external Mg²⁺ from 0 to 6 mm, the vascular smooth muscle mitochondria exhibited respiratory substrate-supported release of Mg²⁺ as studied with metallochromic indicator, eriochrome blue, using dual-wavelength spectrophotometry. The maximal velocity of energized release (3 nmol of Mg²⁺/s/mg of mitochondrial protein) was observed at 4 mm external Mg²⁺ and the half-maximal transport occurred at 0.5 mm.     

The amino acid sequence of chick skin collagen α1-CB7: The presence of a previously unrecognized triplet

Because alignment of the amino acid sequences of chick skin collagen α2-CB3 (1) with the relevant portion of chick skin collagen α1-CB7 (2) suggested that a Gly-X-Y triplet may have been missed in the latter, the peptide TM-2, produced by tryptic digestion of maleylated α1-CB7, was reinvestigated. Cleavage by trypsin at the unblocked lysine at position 18, and isolation of the resulting COOH-terminal peptide, showed this to be a 15-residue peptide containing a previously unrecognized Gly-Pro-Hyp triplet. Sequencing of the peptide showed this to occupy positions 4 through 6, or 56 through 58 of α1-CB7. The latter thus has 271 instead of 268 residues, and the α1[I] chain 1055 instead of 1052.     

Isolation and properties of a ferredoxin from Anabaena Flos-Aquae

Ferredoxin was isolated from the blue-green alga Anabaena flos-aquae. Its homogeneity was shown by conventional and SDS-polyacrylamide gel electrophoresis, and isoelectric focusing on polyacrylamide gel columns, the latter indicating a pI at ca pH 3·7. The absorption spectrum had, in the oxidized state, maxima at 462, 421, 327 and 276 nm, with a shoulder at 284 nm, a spectrum characteristic of plant-type ferredoxins. The 421 : 276 nm absorbance ratio was typically 0.49. The ferredoxin effectively mediated the photoreduction of NADP⁺ by barley chloroplasts depleted of native ferredoxin. The MW obtained by sedimentation-equilibrium and sedimentation velocity-diffusion coefficient studies was ca 12 000 daltons, a value somewhat higher than suggested by amino acid composition data. The ferredoxin contained 2Fe and 2S per molecule.     

THE CONVULSANT ACTION OF METHYLDITHIOCARBAZINATE: A COMPARISON WITH OTHER SULPHUR-CONTAINING HYDRAZIDES

—The convulsant action of methyldithiocarbazinate (MDTC), thiocarbohydrazide (TCH) and thiosemicarbazide (TSC) has been studied in mice. The relationship between dose and time to convulsions indicated that MDTC has a dual action and is more potent than TSC. Pretreatment of mice with pyridoxal phosphate (0.25 mmol/kg) protected against convulsions and death produced by low doses of MDTC or TCH, and low or high doses of TSC. Pretreatment with pyridoxine hydrochloride (0.25 mmol/kg) protected mice against TSC but not against TCH. It protected against low doses of MDTC (0.12 mmol/kg), but shortened the latency to convulsions after intermediate doses of MDTC (0.37 mmol/kg). Glutamate decarboxylase activity (GAD, EC 4.1.1.15) in whole brain homogenates from mice killed at the onset of seizures, was significantly reduced by all 3 drugs at all doses. This inhibition did not exceed 30% after any dose of TSC or TCH, but was 64% in mice killed 4 min after the injection of MDTC (0.98 mmol/kg). The addition of pyridoxal phosphate to brain homogenates abolished GAD inhibition after MDTC but not after TCH. In vitro brain GAD was 50% inhibited by 10⁻⁴m -MDTC, 18% by 10⁻⁴m -TSC and 8% by 10 ⁻⁴m -TCH. Kinetic studies suggested that at low concentrations MDTC inhibits by competing with pyridoxal phosphate. At the onset of convulsions the cerebral content of pyridoxal phosphate was reduced after low or high doses of TSC (0.27 and 2.2 mmol/kg) and after high doses of MDTC (0.98 mmol/kg). All three drugs (at 10⁻⁵−10⁻⁴m ) inhibited pyridoxal phosphokinase (EC 2.7.1.35) in vitro. Short latency convulsions after MDTC (0.37–0.98 mmol/kg) very probably arise from inhibition of cerebral GAD, due to competition for coenzymic sites and/or unavailability of coenzyme. Long-latency convulsions after MDTC (0.12–0.37 mmol/kg) are comparable to those seen after TSC (0.27–2.2 mmol/kg) and may depend on a mechanism additional to inhibition of GAD.     

A cutin acid in Pinus sylvestris microspores

Nonacosan-10-ol (0.7%) and the cutin acid, 9,16-dihydroxyhexadecanoic acid (0.3%) are present in Pinus sylvestris microspores. The pollen coat hence has some features in common with leaf cuticles.     

Reconstitution of pig lymphocyte plasma membranes from solubilized components, with particular reference to membrane-associated immunoglobulins

Plasma membranes of lymphocytes obtained from pig mesenteric lymph nodes were reconstituted after solubilization with bile salts. The proportion by weight of immunoglobulin in the reconstituted membrane was no greater than about 5-10% of that in the original membrane. Possible reasons for the low reincorporation of immunoglobulin are discussed.