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Biomedical subjects

K Koch

Publications and source records attributed to K Koch.

At least 145 records · Page 8Linked to original sources
PubMed1974

Growth control of differentiated fetal rat hepatocytes in primary monolayer culture. VI. Studies with conditioned medium and its functional interactions with serum factors.

Serum-deficient </=0.00003% vol/vol) conditioned medium (CM) obtained from primary cultures of fetal rat hepatocytes initiates DNA synthesis and mitosis in homologous quiescent cultures. CM similarly prepared from 3T3 fibroblast cultures is inactive. At least two conditioning factors are involved in initiating DNA synthesis. The first of these, arginine, is obligatory, synthesized by the cells, and released into the culture medium. The second, a lipid or lipid-containing material, is stable to pH extremes (pH 2, pH 10) and chromatographs with an apparent R(1) approximately 0.5 on silica gel thin-layer plates using hexane-ether (4: 1) as the solvent system. It is suggested that these cultured hepatocytes enter or leave the G(0) or early G(1) phase of the cell cycle as determined in part by their capacity to use available conditioning factor and nutrient components of the medium, in particular, arginine. Serum factors including serum fraction I (4), insulin, and possibly, lipid-like conditioning material appear to initiate DNA synthesis by controlling cellular processes involved with the enhanced utilization and synthesis of growth-limiting nutrients.

Animals↗
PubMed1974

The Effect of Potassium on the Fixation of Molecular Nitrogen by Root Nodules of Vicia faba.

The effect of potassium supply of Vicia faba on the fixation of molecular nitrogen by root nodules was studied by using (15)N-labeled molecular nitrogen. Plants well supplied with potassium showed higher contents of (15)N in the soluble amino fraction and in the protein fraction of various plant organs as compared with plants of a lower potassium status. This effect was evident particularly in the root nodules. Assimilation experiments, carried out with (14)CO(2), revealed that the content of radioactivity in the sugars and amino acids of the root nodules was increased by the potassium supply of the host plants. In particular, the content of (14)C amino acids in the root nodules was influenced beneficially by potassium, which means that potassium favored the provision of reduced nitrogen (NH(3)). It is postulated that the better carbohydrate supply of nodules, by plants well supplied with potassium, results in a higher carbohydrate turnover in the nodules and thus the provision of ATP and reducing electrons required by the nitrogenase is enhanced.

Journal Article↗