Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In variants of the Novikoff hepatoma cell line, the ability to use D-ribose as a carbon source appeared to be due to changes in the expression of ribokinase. Examination of ribokinase activity was prompted by the finding that uptake of radiolabeled ribose was linear for 30 min in six variants but became saturated within 2 min in nine other variants. The linear uptake of ribose was due to a high rate of phosphorylation by ribokinase. Variants which showed linear uptake kinetics had ribokinase levels of 6.8 +/- 1.7 nm/min per mg protein as compared to the parental levels of 0.90 +/- 0.25 nm/min per mg protein. The nine variants which showed saturable uptake kinetics had low parenteal levels of ribokinase. However, these variants showed a change in the subcellular location of that activity. The enzyme was predominantly membrane-associated in both parental cells and high ribokinase variants. In contrast, the low ribokinase variants had a cytoplasmic form of the enzyme. A more general membrane change probably occurred in these variants, since they showed an increased sensitivity to the unrelated membrane reactive compounds, phytohemagglutinin and ouabain.
 ...
PMID:Multiple genetic changes determine ribose utilization by Novikoff hepatoma cell variants. 625 75

Ribokinase, the first enzyme in ribose catabolism, is altered in its expression in ribose-utilizing Novikoff hepatoma variants. 90% of the variants selected for their ability to use D-ribose as a sole carbon source show a change in ribokinase activity. After non-selective growth, phenotypically unstable variants lose their altered expression and regain a parental form of expression of this enzyme. In the variants, ribokinase expression in non-inducible by the carbon source and is unaffected by the growth phase of the cells. However, ribokinase expression in both parental cells and variants is cell cycle-dependent. Parental Novikoff hepatoma cells have three peaks of ribokinase activity during the S, G2 and M phases. Variants are described which have high basal levels of ribokinase and only a single peak of enzymatic activity during the S phase. In addition to changes in the level of ribokinase, changes in the subcellular localization of the enzyme have been found in some variants. While the change in the level of ribokinase seems to be a property of the variant isolated, the change in subcellular location of ribokinase can be readily achieved by culture conditions.
 ...
PMID:Altered expression of ribokinase activity in Novikoff hepatoma variants. 628 3