On the antisymmetry of the amino acid code table

Antisymmetry of the amino acid code table in terms of codon degeneracy is pointed out, and it is related to a physico-chemical problem of codon-anticodon interaction energy. A strong negative correlation between molecular weight of an amino acid and its codon degeneracy is pointed out, and its implication to the origin of the amino acid code table is discussed. Finally, an earlier form of the amino acid code table is proposed.     

Estimation of growth yield and maintenance coefficient of plant cell suspensions

Methodology is presented for the determination of growth yield (Y(g)) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Y(g) and m requires measurements of specific growth rate (micro) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Y(g) and m because micro is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the K(m) for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the K(m), the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Y(g) and m because various steady-state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of micro and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.     

Difference in superoxide toxicity between 4,7-dicyanobenzofurazan and paraquat.

The O2-. production by aerobically cultured Escherichia coli in the presence of benzofurazan (1), 4,7-dimethylbenzofurazan (2), 4,7-dibromobenzofurazan (3), 4-bromo-6-cyanobenzofurazan (4), and 4,7-dicyanobenzofurazan (5) was examined by using the cytochrome c reduction method in order to elucidate the mechanism of cytotoxicity of benzofurazans. Adding compound 5 to E. coli cell suspension caused cytochrome c reduction, which was completely inhibited by superoxide dismutase. The rate of cytochrome c reduction was in the order of 1 = 2 = 3 less than 4 less than 5, which correlates well with that of the reduction potentials of these benzofurazans. Adding glucose to the E. coli cell suspension-compound 5-cytochrome c system accelerated the rate of cytochrome c reduction. The formation of 4,7-dicyanobenzofurazan anion radical in the cell suspension-compound 5-glucose system in the absence of O2 was followed by ESR spectroscopy. The ESR signal of the anion radical disappeared when O2 was added. Compound 5 was shown to have an approximately 10-fold greater increasing effect on the flux of O2-. by E. coli than paraquat (PQ) by the cytochrome c reduction method. The results were confirmed by the electrochemical method with an oxygen electrode. However, compound 5 had a bacteriostatic, but not lethal, effect, while PQ had both effects. The effect of compound 5 and PQ on lethality of E. coli showed a dramatic difference when E. coli was exposed to these two compounds and washed prior to testing the effects of that exposure. This difference probably arose because compound 5 readily leaked from the cells during dilution and plating. Also, the reduced form of compound 5 exits from the cells more readily than the reduced form of PQ and then generates O2-. in the medium by autoxidation. This suggests the importance of the intracellular production of O2-., rather than the extracellular production of O2-., for lethal effect.     

Sphingolipids are essential for the growth of Chinese hamster ovary cells. Restoration of the growth of a mutant defective in sphingoid base biosynthesis by exogenous sphingolipids.

We previously isolated a temperature-sensitive Chinese hamster ovary cell mutant (strain SPB-1) with thermolabile serine palmitoyltransferase, which is involved in the first step of sphingolipid synthesis (Hanada, K., Nishijima, M., and Akamatsu, Y. (1990) J. Biol. Chem. 265, 22137-22142). In this study, sphingolipid-deficient culture medium was used to examine the effect of exogenous sphingolipids on the cell growth of SPB-1. When cultivated in the sphingolipid-deficient medium, SPB-1 cells ceased growing at non-permissive temperatures. Under these conditions, de novo sphingolipid synthesis ceased in the SPB-1 cells, resulting in a decrease in levels of sphingomyelin and ganglioside sialyl lactosylceramide (GM3), whereas the parental CHO-K1 cells grew logarithmically with normal sphingolipid synthesis. Exogenous sphingosine restored the contents of both sphingomyelin and GM3 in the SPB-1 cells near to the parental levels through metabolic utilization and allowed the mutant cells to grow even at the non-permissive temperature. Similarly, exogenous sphingomyelin restored the sphingomyelin levels and only partly the GM3 levels and also suppressed the temperature-sensitivity of the SPB-1 cell growth. In contrast, exogenous glucosylceramide, which restored the GM3 levels but not the sphingomyelin levels, failed to suppress the temperature sensitivity of the SPB-1 cell growth. Combination of exogenous sphingomyelin with ceramide, glucosylceramide, GM3, or sphingoid bases did not show any synergistic or additive effect on the SPB-1 cell growth enhancement, compared with sphingomyelin alone. The results indicated that the temperature sensitivity of the SPB-1 cell growth was due to the lack of cellular sphingolipids, possibly that of sphingomyelin.     

Expression of the human angiotensinogen gene in transgenic mice and transfected cells.

We have generated two lines of transgenic mice with integrated copies of a 14-kilobase pair (kb) human DNA fragment containing the angiotensinogen gene, which includes 1.3 kb of 5'- and 3'-flanking regions. In both transgenic lines, a considerable quantity of the correctly initiated and processed angiotensinogen mRNA was detected in the liver and it was detectable in heart. Unexpectedly, mRNA for the transgene was accumulated in the kidney, where is normally the minor source of angiotensinogen, to levels comparable to that in the liver. In addition, an in vitro transfection analysis suggested that the 1.3-kb 5'-flanking sequences are essential for expression of the angiotensinogen gene in hepatic and renal cells and that neither DNA segment within the 14-kb construct contributes significantly to repression of the gene expression in renal cells.