Peptides from plant tissues

Giavalisco, P., Nordhoff, E., Lehragh, H., Gobom, j., Klose, j., Mueller, M., Egelhoeer, V., Theiss, D., Seitz, H. (2003). Extraction of proteins from plant tissues for two-dimensional electrophoresis analysis A calibration method that simplifies and improves accurate determination of peptide molecular masses by MALDl-TOE MS. Electrophoresis 24, 207-216. 

P-Endorphin. A peptide corresponding to the 31 C-terminal amino acids of P-LPH was first discovered in camel pituitary tissue (10). This substance is P-endorphin, which exerts a potent analgesic effect by binding to cell surface receptors in the central nervous system. The sequence of P-endorphin is well conserved across species for the first 25 N-terminal amino acids. Opiates derived from plant sources, eg, heroin, morphine, opium, etc, exert their actions by interacting with the P-endorphin receptor. On a molar basis, this peptide has approximately five times the potency of morphine. Both P-endorphin and ACTH ate cosecreted from the pituitary gland. Whereas the physiologic importance of P-endorphin release into the systemic circulation is not certain, this molecule clearly has been shown to be an important neurotransmitter within the central nervous system. Endorphin has been invaluable as a research tool, but has not been clinically useful due to the avadabihty of plant-derived opiates. 

Plant defensins are cystine-rich, cationic peptides ranging in size from 45 to 54 amino acids, of which eight are cysteine. They were first discovered in wheat and barley ° and were proposed to form a novel subclass of thionins, the 7-thionins. As it became clear that they closely resemble mammalian and insect defensins in primary and secondary structure, the term plant defensins was introduced to describe these peptides. It is generally assumed that all plants express plant defensins " and that they are expressed in a wide range of plant tissue, that is, leaves, floral tissue,tubers,bark, root, pods, and seeds,with seeds in particular being from where most plant defensins have been isolated. ... 

Cyclotides have been isolated from many plant tissues, including leaves, stems, flowers, roots, and Recently, the levels of the Mobius-type cyclotide kalata B1 were quantified in various plant tissues of the Rubiaceae family plant Oldenlandia affinis by Seydel and Dornenburg. They found raised levels of kalata B1 in shoot tips and leaves, while flowers and stems contained significantly lower levels of the peptide. 

The purpose of this article was to review peptides with more than one biological activities and to show that peptide-hormones and neuropeptides are implicated in more than one biological function including that of cancer. In addition, many other naturally occurring peptides isolated from animal / human and plant tissues where found to exert at least a second biological effect. 

To study these proteins further we developed methods for the hydrolysis of lAA-peptides without their extraction from the plant material. This was necessitated also in order to evaluate extraction efficiency. Other macromolecules containing lAA might not be extracted under the particular conditions employed, and without the ability to determine a true value for total lAA the presence of such species was difficult to predict. In addition, we were interested in extending these investigations to other plant tissues and to other species where the solubility of macromolecular conjugates, if present, would be unknown (Fig. 1). Instead of extraction of the tissue followed by hydrolysis of the extracted conjugate, we... 

Resistance to Proteolysis. As the peptides were expected to be either secreted from plant cells in transgenic plants or applied to the external surfaces of plant tissues, the extracellular proteases present in the intercellular spaces of plant tissues were considered to be most important. Accordingly, peptides were tested against crude preparations of enzymes from the extracellular fluid (ECF) of plant leaves. Extracellular fluids from leaves of maize, tobacco and potato, and spent medium from cultured plant cells produced similar results tobacco ECF was used routinely. 

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