Accurate assay of dopa decarboxylase by preventing nonenzymatic decarboxylation of dopa

The nonenzymatic decarboxylation of dopa was completely blocked by both 2-mercaptoethanol and EDTA together over the wide range of pH. This finding made it possible to measure the activity of dopa decarboxylase precisely even at an alkaline pH value. The pH optimum of dopa decarboxylase was found to be pH 7.0 and the Km value for dopa was determined to be 4 X 10(-5) M.     

Effects of Light on Dopamine Metabolism in the Chick Retina

The effect of prolonged exposure to light on the activity of dopaminergic neurons and dopamine (DA) metabolism of chick retinae was investigated. alpha-Fluoromethyldopa, a potent and specific irreversible inactivator of aromatic amino acid decarboxylase, was used to assess DA turnover after inhibition of synthesis, and also to assess in vivo tyrosine hydroxylase activity by dihydroxyphenylalanine accumulation. After 48 h of light exposure, retinal DNA in 12-day-old chicks was about 30% higher (p less than 0.005) whereas dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were elevated two to three times (p less than 0.005) the level of controls kept in the dark for the same period. DA turnover was about twofold faster in the light (t 1/2 = 31 min) than in the dark (t 1/2 = 65 min). Tyrosine hydroxylase, assayed in vitro with saturating levels of cofactor and substrate, increased by about 50% after light exposure. The apparent tyrosine hydroxylase activity in vivo was approximately sixfold higher in the light than the dark. These results are interpreted and discussed in terms of the regulation of DA synthesis, and the use of DOPAC and HVA as indices of DA function in the retina.     

Induction of sexual reproduction in Opalina sudafricana by injecting its host Bufo regularis with gibberellic acid

Induction of sexual reproduction in Opalina sudafricana by injecting its host Bufo regularis with gibberellic acid. International Journal for Parasitology4, 203–206. Opalina sudafricana parasitic in the rectum of Bufo regularis was induced to reproduce sexually when its host was injected subcutaneously with 0·3 mg of gibberellin-A₃. This plant growth substance had no effect on the induction of encystation in the parasites in vitro. Urine of toads injected with gibberellin-A₃ induced sexual reproduction (encystation) in the opalinids in vitro. It is speculated that the plant hormone must either be broken down into an active substance by the toad or cause the toad to excrete its own gonadal hormones (or other hormones) into the urine. This active substance or the excreted hormones may induce division in the parasites resulting in the formation of small forms which encyst.     

Puromycin aminonucleoside increases the synthesis of ribonuclease inhibitor and other proteins in kidney

The incorporation of labelled amino acids into proteins was measured in vivo in the kidney of control rats and rats that received puromycin aminonucleoside. There was an increase in the synthesis of kidney proteins after the aminonucleoside that was similar to the increased synthesis previously observed in cell-free and slice preparations. The increased synthesis in vivo and in vitro especially involved proteins of the prealbumin fraction of average molecular weights of approx. 50 000, 35 000, 25000, 18 000, and 10 000. The largest of these proteins was identified as kidney ribonuclease inhibitor and additional evidence was obtained for the increased synthesis of the kidney inhibitor after aminonucleoside.     

Energetics of cell-cell and cell-biopolymer interactions

The energy vs distance balance of cell suspensions (in the presence and in the absence of extracellular biopolymer solutions) is studied, not only in the light of the classical Derjaguin-Landau-Verwey-Over-beek (DLVO) theory (which considered just the electrostatic (EL) and Lifshitz-van der Waals (LW) interactions), but also by taking electron-acceptor/electron-donor, or Lewis acid-base (AB) and osmotic (OS) interactions into account. Since cell surfaces, as well as many biopolymers tend to have strong monopolar electron-donor properties, they are able to engage in a strong mutual AB repulsion when immersed in a polar liquid such as water. The effects of that repulsion have been observed earlier in the guise of hydration pressure. The AB repulsion is, at close range, typically one or two orders of magnitude stronger than the EL repulsion, but its rate of decay is much steeper. In most cases, AB interactions are quantitatively the dominant factor in cell stability (when repulsive) and in “hydrophobic interactions” (when attractive). OS interactions exerted by extracellularly dissolved biopolymers are weak, but their rate of decay is very gradual, so OS repulsions engendered by biopolymer solutions may be of importance in certain long-range interactions. OS interactions exerted by biopolymers attached to cells or particles (e.g., by glycocalix glycoproteins), are very short-ranged and usually are negligibly small in comparison with the other interaction forces, in aqueous media.     

高胆固醇高脂肪膳食对家兔β-VLDL组成及其与巨噬细胞相互作用的影响的初步研究

给家兔喂以1％胆固醇及10％菜油(A组)或猪油(B组)50多天后A组血胆固醇水平(824.2±265.1mg/dl)明显低于B组(1666±693.8mg/dl);A组甘油三酯水平(51.9±19.1mg/dl)亦低于B组(104±40.2mg/dl)。二组家兔的β—VLDL的脂类组成无差别,但A组β—VLDL的apoE高于B组,分别为45.2％及37.5％。高分子量apoB(apoB_h)为33.6％,低于B组β-VLDL(47.3％)。A组β-VLDL促进小鼠腹腔巨噬细胞胆固醇堆积的程度大于B组,可能与apoE含量高有关。我们认为多不饱和脂酸减轻动脉粥样硬化(As)的作用不在于改变脂蛋白构成后阻碍泡沫细胞的形成而是促进β—VLDL从体内清除。     

Effect of retinoic acid on the proliferation and tumorigenicity of mouse mastocytoma cells

Retinoic acid (RA) inhibited the in vitro growth of the mouse mast cell tumor line P₈₁₅ in a dose- and time-dependent manner. The inhibition was accompanied by an increase in the amount of neutral intracellular mucopolysaccharides. Study of cell cycle kinetics showed that exposure to retinoic acid led to a slowing-down of the cell-cycle progression possibly related to a more differentiated cell population disclosed by microscopy with a lower proliferative capacity. In vivo, delays in both tumor appearance and mouse mortality were observed after injecting RA into mice bearing mastocytomas. These results suggest that RA could be of interest in the treatment of human malignant systemic mastocytosis with proliferation of immature mast cells.     

Plant hormone response mutants

A variety of plant hormone response mutants has now been described, and is surveyed in this article. In addition to hormone-insensitive mutant phenotypes with defects in hormone-related features, there exist mutants apparently constitutive for the gibberellin responses, and also a mutant hyper-responsive to gibberellin. Although there is still little biochemical evidence on the nature of these mutants, the emerging picture of their genetic dominance relationships has given rise to tentative suggestions of the involvement of represser functions in hormonal control systems.