Ultraviolet-mediated cytotoxic activity of phenylheptatriyne from Bidens pilosa L.

The tropical weed Bidens pilosa L. (Asteraceae) contains a number of polyacetylenes which are phototoxic to bacteria, fungi, and human fibroblast cells in the presence of sunlight, artificial sources of long-wave ultraviolet light, or cool-white fluorescent light. The principle photoactive compound in the leaf, phenylheptatriyne, is present in the cuticle as well as in the underlying cells. Experiments with calf thymus DNA indicate that, unlike photoactive furanocoumarins, phenylheptatriyne does not form interstrand cross linkages with DNA in ultraviolet light.

Effect of benzimidazole on nicotinamide adenine dinucleotide phosphate phosphomonoesterase activity in wheat leaves.

Nicotinamide adenine dinucleotide phosphate phosphomonoesterase was isolated and partially purified from wheat (Triticum aestivum L. var. Selkirk) leaves. The enzyme had KNADP value of 1.4 X 10(-4) M and a pH optimum of 5.9. In vitro activity of this enzyme was unaffected by precursors of NAD (nicotinamide and nicotinic acid) or cytokinins (kinetin and benzimidazole). However, when detached wheat leaves were treated with solutions of these compounds, the precursors lowered the specific activity while the cytokinins enhanced the activity. It is suggested that spatial separation and compartmentation of the enzyme and its substrate NADP account for the similar effect of benzimidazole on both.

Isocitrate lyase in green leaves.

Isocitrate lyase (EC 4.1.3.1) has been demonstrated in crude dialyzed extracts of healthy spinach (Spinacia oleracea) leaves from commercial sources and wheat (Triticum aestivum) and maize (Zea mays) leaves stored in darkness in the cold room for 1 week. The products of the reaction were identified as glyoxylate and succinate, the former by its phenylhydrazone, and the latter traced by isotopic labeling and cochromatography. Fresh spinach extracts contain a mixture of at least two endogenous inhibitors of isocitrate lyase activity and one of them is proteinaceous. The endogenous inhibitor(s) is thermostable and retains 50% of its inhibitory effect even after boiling for 10 minutes. Dark starvation of the leaves removes the inhibition, due possibly to autolysis of the inhibitor(s). The inhibitor(s) can also be removed by filtration through Sephadex gels. The crude extract from spinach shows double pH optima in phosphate buffer at pH 7.4 and pH 8.0. The apparent Km at pH 7.4 was 0.1 mm. Oxaloacetate, dl-malate, succinate, 3-phosphoglycerate, and glycolate at 10 mm concentration inhibited, but ribulose 1,5-diphosphate activated enzymic activity.