Differentiating effect of L-tyrosine on the human melanoma cell line IIB-MEL-J

IIB-MEL-J is a highly heterogeneous newly established human melanoma cell line. The addition of 3 mM L-tyrosine to the culture medium produced (1) a great decrease in the cell growth rate, (2) a loss of the anchor-age-independent growth capacity, and (3) a change in the morphology of the cells to a fibroblastoid aspect. Coincident with these changes, an increase in subpopulations I and II and a decrease in subpopulations III and IV took place. In view of this evidence we consider that the cells have differentiated. The melanin production was not increased by the L-tyrosine treatment, suggesting that differentiation and melanin expression are not strictly correlated.     

CO2 Incorporation and 4-Hydroxy-2-Methylbenzoic Acid Formation during Anaerobic Metabolism of m-Cresol by a Methanogenic Consortium

The metabolism of m-cresol by methanogenic cultures enriched from domestic sewage sludge was investigated. In the initial studies, bromoethanesulfonic acid was used to inhibit methane production. This led to the accumulation of 4.0 ± 0.8 mol of acetate per mol of m-cresol metabolized. These results suggested that CO₂ incorporation occurred because each molecule of m-cresol contained seven carbon atoms, whereas four molecules of acetate product contained a total of eight carbon atoms. To verify this, [¹⁴C]bicarbonate was added to bromoethanesulfonic acid-inhibited cultures, and those cultures yielded [¹⁴C]acetate. Of the label recovered as acetate, 89% was found in the carboxyl position. Similar cultures fed [methyl-¹⁴C]m-cresol yielded methyl-labeled acetate. A ¹⁴C-labeled transient intermediate was detected in cultures given either m-cresol and [¹⁴C]bicarbonate or bicarbonate and [methyl-¹⁴C]m-cresol. The intermediate was identified as 4-hydroxy-2-methylbenzoic acid. In addition, another metabolite was detected and identified as 2-methylbenzoic acid. This compound appeared to be produced only sporadically, and it accumulated in the medium, suggesting that the dehydroxylation of 4-hydroxy-2-methylbenzoic acid led to an apparent dead-end product.     

Effect of water potential on seed germination

The response of seed germination to substrate water potential was determined for several plant species of the arctic tundra. Seeds were collected from Cape Thompson and Eagle Summit, Alaska and germinated on dialysis membranes over water solutions of polyethylene glycol with osmotic potentials of 0 to −6 bars. Germination did not occur with potentials below −3 bars, except for three fellfield species. Germination was delayed at lower osmotic potentials. Because the response of most species was similar, substrate water potential is probably not a factor affecting the establishment of most tundra plant species from seeds.     

C-methyl phenolics from Qualea species

The trunk wood of Qualea labouriauana contains, besides (2R)-5,7,4′-trihydroxy-3′-methoxy-6,8-dimethylflavanone, (2R)-5,7,4′-trihydroxy-8-methylflavanone, the biosynthetically interesting 2,2′-dihydroxy-4,6,4′,6′-tetramethoxy-3,3′-dimethylbenzophenone. From the trunk wood extract of Q. paraensis the first named flavanone crystallized out directly.     

Dinoflagellate sterols IV: Isolation and structure of 4α,23ξ,24ξ-trimethylcholestanol from the dinoflagellate Glenodiniumhallii

The dinoflagellate $\text{Glenodinium}$$\text{hallii}$ was investigated for its sterol composition. Five of the six sterols were isolated and identified as cholest-5-en-3β-ol, (24ξ)-24-methylcholest-5-en-3β-ol, stigmasta-5,22-dien-3β-ol, (22E,24R)-4α,23,24-trimethyl-5α-cholest-22-en-3β-ol, and 4α,23ξ,24ξ-trimethyl-5α-cholestan-3β-ol.     

Serum lipoproteins and albumin in the lecithin: Cholesterol acyltransferase reaction

The unique features of pig ovarian follicular fluids, i.e., presence of high density lipoprotein (HDL) only and lecithin: cholesterol acyltransferase (EC 2.3.1.43; LCAT) activity, provides a good model to study the effect of serum lipoproteins and serum albumin on the LCAT reaction. $\text{In}\text{vitro}$ cholesterol esterification is enhanced when very low density lipoprotein (VLDL) and low density lipoprotein (LDL) fractions are added, but is inhibited when one or the other of these lipoproteins is absent. High concentrations of HDL₂ result in decreased activation which can be compensated for by the addition of the VLDL-LDL mixture. These findings suggest that the rate of cholesterol esterification in ovarian follicular fluid may be enhanced by providing the exogenous VLDL and LDL as the recipients of HDL-cholesteryl ester. The inhibition of LCAT activity caused by free fatty acid and lysophosphatidylcholine can be partially reversed by the addition of serum albumin, suggesting that serum albumin may regulate the LCAT reaction.     

The mechanism of action of Cu2+ on the frog skin.

The mechanism of action of Cu2+ when applied to the external side of the frog skin preparation was investigated. Cu2+ acts most probably on the external barrier of this preparation, since it increases the transport pool of Na+ proportionally to the increase in the short circuit current (Isc). Cu2+ does not open new routes for the Na+ entry since the stimulated Isc is still completely abolished by amiloride. The Isc dependence of Na+ concentration in the external medium is modified by copper, since the Km value increases in addition to changes in V. It is suggested that copper acts at the external barrier Na channels in a way similar to that proposed by Zeiske and Lindemann ((1974) Biochim. Biophys. Acta 352, 323--326) for benzoylimidazole-2 guanidine and benzoylthiazole-2 guanidine and by Dick and Lindemann ((1975) Pflügers Arch. ges. Physiol. 355, R72) for para-chloromercuribenzenosulfonate and para-chloromercuribenzoate.     

The effect of copper on frog skin. The role of sulphydryl groups

1. 1. Cu²⁺ at a concentration of 10⁻⁴ M, when applied to the external side of the frog skin produces an increase in the short-circuit current (I_sc).

2. 2. This effect was studied in skins of Rana temporaria adapted to cold (5°C) and room temperature (20°C), skins of Rana pipiens adapted to cold, and the results compared with those obtained previously with Rana ribibunda.

3. 3. The observed effect is less dependent upon the adaptation to cold than upon the functional state of the skin: skins with low short circuit currents have a bigger response to Cu²⁺ than skins with high I_sc.

4. 4. A species difference cannot be ruled out since skins of Rana ribibunda exhibiting high I_sc give good responses to Cu²⁺.

5. 5. 5,5′-dithiobis(2-nitrobenzoic acid), a sulphydryl-oxidizing reagent, produces an effect similar to that of Cu²⁺, and dithiothreitol an SH-reducing agent, reverses the effect of this ion.

6. 6. Cu²⁺ also induces an increase in the unidirectional K⁺ fluxes and unmasks a net outward potassium flux.

7. 7. The outward K⁺ flux induced by Cu²⁺ is sensitive to ouabain.

8. 8. It is concluded that Cu²⁺ increases the permeability of the external barrier of the frog skin to Na⁺ and K⁺, probably by reacting with SH groups.

Physical properties and Tris inhibition of an insect trehalase and a thermodynamic approach to the nature of its active site

The midgut from Rhynchosciara americana larvae display a trehalase (alpha,alpha'-trehalose glucohydrolase, EC 3.2.1.28) which is soluble with a molecular weight of 122 000 and pI 4.6. The optimum pH of the enzyme is 6.0, its apparent Km for trehalose is 0.67 mM and its energy of activation is 16.7 kcal/mol. Sulfhydryl reagents do not inhibit the trehalase. The results suggest the existence of two carboxyl groups in the active site, one of which has a very high (8.3) pK. The increase of the pK values of the essential groups of the free enzyme in the presence of increasing concentrations of dioxane supports the hypothesis that these groups are carboxyls. The purified enzyme hydrolyzes only alpha,alpha'-trehalose and it is competitively inhibited by several compounds.     

Rapid and efficient separation and identification of the two molecular forms of human adenosine deaminase by thin-layer gel filtration chromatography

Two molecular forms of adenosine deaminase have been found in human tissues. The column gel filtration method has been used for the separation of the two enzyme forms. Routine separation and analysis of the enzyme forms based on the molecular size difference can be achieved by thin-layer gel filtration on Sephadex G-200 superfine gel. The thin-layer method has been found to be more rapid and efficient than the column method. Enzymes in crude preparations can be studied effectively with the thin-layer method.