Protein synthesis in the intestine of goldfish acclimatized to different temperatures

1. The incorporation of [¹⁴C]valine and [³H]threonine has been studied in mucosa of goldfish acclimatized to different temperatures. 2. [¹⁴C]Valine was incorporated more rapidly than [³H]threonine at acclimatization temperatures below 15°; this distinction disappeared at higher temperatures. 3. The rate of amino acid incorporation rose as the environmental temperature was increased. 4. The number of valine residues in mucosal protein fell and the number of methionine residues rose as the acclimatization temperature was raised. 5. The concentration of free methionine was closely related to the amount in protein in goldfish mucosa; both increased at higher acclimatization temperatures. 6. An attempt is made to show that these changes are integrated with possible homoeostatic mechanisms in the goldfish intestine.     

The site of synthesis of mitochondrial proteins in Krebs II ascites-tumour cells

At 22° in Earle's medium, Krebs cells synthesize proteins. After a brief `pulse' with [<sup>14</sup>C]valine followed by a `chase' of [¹²C]valine the radioactivity appears first in microsomes and is transferred after `chase' to the cell sap. Kinetics of labelling of the mitochondrial protein are different from that of either microsomal or cell-sap protein. When Krebs cells in buffer are mixed with ribonuclease in water the nuclease penetrates the cell membrane. The ribonuclease-treated cells are still viable but have lost most of their cytoplasmic ribosomes (electron micrograph). Such cells still synthesize mitochondrial protein at near normal rate but synthesis of microsomal protein is severely inhibited. The results indicate that some mitochondrial proteins are synthesized independently of the microsome–cell-sap system.     

关节炎疾病的分子反应机理

引起类风湿性关节炎疼痛、浮肿的病因机制,现已有了一定的了解。伦敦西部的CharingCross Sunley研究中心的医学家们在风湿性关节炎患者的关节处发现了关节炎症的分子反应机理。作出这一发现的免疫学小组负责人,Marc Feldmann乐观地认为,该发现最终将有助于     

甲烷氧化细菌的一个新种

从沼气发酵装置中,分离出一株H型专性甲烷氧化细菌81Z菌株。它具有甲烷氧化细菌的一般典型性状。根据其极生单鞭毛和过氧化氢酶阴性的特征,该菌株明显地区别于已知的任何一种甲烷氧化细菌,被认为是一个新种并命名为沼气甲基弯菌(Methylosinus methanica)。本文还讨论了它在厌氧条件下的生命活动。     

Oxygen and Hydrogen Isotope Fractionation during Cellulose Metabolism in Lemna gibba L

Lemna gibba L. B3 was grown under heterotrophic, photoheterotrophic, and autotrophic conditions in water having a variety of hydrogen and oxygen isotopic compositions. The slopes of the linear regression lines between the isotopic composition of water and leaf cellulose indicated that under the three growth conditions about 40, 70, and 100% of oxygens and carbon-bound hydrogens of cellulose exchanged with those of water prior to cellulose formation. Using the equations of the linear relationships, we estimated the overall fractionation factors between water and the exchanged oxygen and carbon bound-hydrogen of cellulose. At least two very different isotope effects must determine the hydrogen isotopic composition of Lemna cellulose. One reflects the photosynthetic reduction of NADP, while the second reflects exchange reactions that occur subsequent to NADP reduction. Oxygen isotopic composition of cellulose apparently is determined by a single type of exchange reaction with water. Under different growth conditions, variations in metabolic fluxes affect the hydrogen isotopic composition of cellulose by influencing the extent to which the two isotope effects mentioned above are recorded. The oxygen isotopic composition of cellulose is not affected by such changes in growth conditions.