Polyphenol oxidase (PPO) arm of catecholamine pathway catalyzes the conversion of L-tyrosine to L-DOPA in Mucuna pruriens (L.) DC var. pruriens: An integrated pathway analysis using field grown and in vitro callus cultures

Mucuna pruriens (L.) DC var. pruriens is the natural source for _L-DOPA, precursor of the neurotransmitter dopamine, used widely in the treatment of Parkinson's disease. However, _L-DOPA synthesis in plants is mediated either by Catecholamine (CA) pathway or alternate pathway catalyzed by Cytochrome P450 (CYP450) class of enzymes. Interestingly, the CA pathway itself can be initiated either by tyrosine hydroxylase (TH) or polyphenol oxidase (PPO). The CA pathway mediated synthesis of _L-DOPA has not yet been proved in M. pruriens albeit strong indications. Therefore, the present investigation is focused on metabolite analysis of major intermediates of CA pathway up to the formation of dopamine and expression analysis of the selected genes, in different tissues and callus cultures. The four major intermediates, _L-tyrosine, tyramine, _L-DOPA and dopamine, were detected using NMR spectroscopy and quantified by HPLC in the callus cultures and in different tissues of the field plant, respectively. The various stages of leaf tissue were also analyzed for metabolite profiling. The relative amount of intermediates detected during the ontogeny of leaf indicates that PPO mediated conversion of _L-tyrosine to dopamine through _L-DOPA is relatively higher compared to dopamine production from tyramine. Among the two possible enzymes, activity of PPO was 6.5-fold more than TH in metabolically active young leaves compared to intermediate leaves. The gene expression profiles comprising upstream genes of _L-tyrosine synthesis and downstream up to dopamine synthesis shows strong correlation with _L-DOPA synthesis. The study validates CA pathway mediated synthesis of _L-DOPA with PPO as candidate enzyme, in M. pruriens.

Trapping, manipulation, and crystallization of live cells using magnetofluidic tweezers

Live mammalian cells are captured and manipulated in magnetofluidic traps created in a suspension of biocompatible, magnetic nanoparticles by a coaxial magnetic/non-magnetic "micropen". Upon activation by an external electromagnet, the pen creates microscale gradients of magnetic field and nanoparticle concentration that translate into directional and confining forces acting on the cells. Both individual cells and cell collections can be trapped by this method, allowing, for instance, for the formation of regularly shaped cell assemblies. The method does not entail any local heating artifacts and does not require magnetic tagging of the cells.

Hypericin biosynthesis in Hypericum hookerianum Wight and Arn: investigation on biochemical pathways using metabolite inhibitors and suppression subtractive hybridization

The biochemical pathway to hypericin biosynthesis is presumed to be polyketide synthase (PKS) mediated, but it has not been experimentally validated, and no alternate route (chorismate/o-succinylbenzoate pathway) has been analyzed. We report here our earlier developed auxin inducible culture systems of Hypericum hookerianum as a model, to study the metabolic pathway to hypericin synthesis. Inhibitors of the alternate pathway at varying concentrations showed steady synthesis of total hypericins with means of 2.80±0.22, 18.75±0.01; 16.39±3.75, 29.60±1.90 (mevinolin) 2.53±0.10, 18.12±0.56; 0.14±0.01, 14.28±1.11 (fosmidomycin) and 2.7±0.35, 18.75±0.61; 0.14±0.01, 12.80±1.09 mg g(-1) DW (glyphosate) in the control and auxin-induced shoot and shoot-forming callus cultures, respectively. SSH analysis classified the differentially expressed sequences into protein synthesis (38%), modification (20%), electron transport (9%) and remaining as unclassified (11%) and unknown proteins (22%). Functional annotation of sequences indicates the presence of additional protein components besides PKS activity. Our results demonstrate direct biochemical and molecular evidence of PKS hypothesis of hypericin biosynthesis for the first time.