Purification of Hydrogenase from Chlamydomonas reinhardtii

A method is described which results in a 2750-fold purification of hydrogenase from Chlamydomonas reinhardtii, yielding a preparation which is approximately 40% pure. With a saturating amount of ferredoxin as the electron mediator, the specific activity of pure enzyme was calculated to be 1800 micromoles H₂ produced per milligram protein per minute. The molecular weight was determined to be 4.5 × 10⁴ by gel filtration and 4.75 × 10⁴ by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme has an abundance of acidic side groups, contains iron, and has an activation energy of 55.1 kilojoules per mole for H₂ production; these properties are similar to those of bacterial hydrogenases. The enzyme is less thermally stable than most bacterial hydrogenases, however, losing 50% of its activity in 1 hour at 55°C. The K_m of purified hydrogenase for ferredoxin is 10 micromolar, and the binding of these proteins to each other is enhanced under slightly acidic conditions. Purified hydrogenase also accepts electrons from a variety of artificial electron mediators, including sodium metatungstate, sodium silicotungstate, and several viologen dyes. A lag period is frequently observed before maximal activity is expressed with these artificial electron mediators, although the addition of sodium thiosulfate at least partially overcomes this lag.     

DNA content in the genus Xenopus

Nuclear DNA amounts were determined by cytofluorometry for twelve species and subspecies of the genus Xenopus. Absolute values, in pg per nucleus, were obtained by direct comparison with human lymphocyte nuclei. The lowest DNA amount (3.55 pg) was found in X. tropicalis, which possess only 20 chromosomes, and the highest (16.25 pg), in the hexaploid X. ruwenzoriensis, with 108 chromosomes. The two recently discovered tetraploid species, X. sp.n. and X. vestitus have, respectively, 12.57 and 12.83 pg of DNA. Among the species and subspecies with 36 chromosomes, the DNA content ranges from 6.35 to 8.45 pg.     

Biology of the minnow Phoxinus phoxinus and its interactions with brown trout Salmo trutta in Øvre Heimdalsvatn, Norway

Minnows have recently been introduced into the mountain lakes of southern Norway. In Øvre Heimdalsvatn, an intensively studied lake, the minnow population has increased rapidly during the last decade. Studies were performed on feeding habits, habitat preferences, age, growth, energy content, densities, parasites, predation and spawning activities. Several aspects were found to be different from other studies, e.g. higher age of sexual maturation, lower growth rate, no feeding on plants, and low infection of parasites. The interaction with the only other fish, the brown trout, is discussed in relation to the minnow population. In 1978 the minnows constituted little more than 10% of production and food consumption of the trout population, and only limited food competition and predation was documented. Increasing competition is likely with a greater minnow population.     

The role ofH-2 regions in overcoming tissue incompatibility

Neonatal transplantation tolerance to the products of theH-2 ^b complex was induced in B10.A (H-2 ^a ) mice. On the basis of the survival of skin allografts it was found that antigens determined by theD region of theH-2 ^b complex (of the B10.A(2R) strain) were most easily overcome and that tolerance to the products of theD end of theH-2 complex (of the B10.A(4R) strain) was also easy to induce. The antigens produced by theK end ofH-2 (of the B10.A(5R) and B10.A(3R) strains) represented a stronger incompatibility barrier and a difference in the entireH-2 ^b complex caused strongest resistance to tolerance induction. When tolerance to the products of the entireH-2 ^b complex was induced in newborn B10.A mice, and the neonatally treated animals were grafted simultaneously with five different grafts, those disparate at theK end ofH-2 and in the entireH-2 region were rejected in some animals, while the grafts disparate at theD end of H-2 remained intact in the same mice. No dependence on theI-J subregion was observed in this system. Furthermore, tolerance was more easily inducible in male than in female B10.A mice.     

Detection and regulation of δ-aminolevulinic acid synthetase activity in rat skeletal muscle

The presence of δ-aminolevulinic acid synthetase (ALAS) in mitochondria obtained from rat skeletal muscles has been observed. Optimal conditions for the meausurement of this activity are described. The activity of skeletal muscle ALAS was investigated under conditions known to affect the activity of this enzyme in other tissues. ALAS activity in skeletal muscle mitochondria was decreased 55% by a 48-h fast. Treatment with dexamethasone did not reverse the effect of starvation on ALAS activity and did not change the activity in the fed controls. ALAS activity was decreased 56% in skeletal muscle mitochondria obtained from rats in which diabetes mellitus had been induced by streptozotocin. Administration of insulin to the diabetic animals partially reversed the effect of diabetes on skeletal muscle ALAS; however, administration of insulin to control animals caused a 21% decrease in skeletal muscle ALAS activity. By contrast, treatment with inducers of hepatic ALAS such as allylisopropylacetamide or 3,5-dicarbethoxy-1,4-dihydrocollidine had no effect on skeletal muscle ALAS. These results confirm our previous suggestion that ALAS activity is regulated in a tissue-specific manner.