Polyamines hormones

One of the insect neurohormones, the activation hormone, controls the secretion of the corpora allata, paired glands that synthesize the juvenile hormone (Fig. 22-4) in insect larvae. While the structure of the juvenile hormone varies somewhat with species, it is usually a polyprenyl ester. A specific binding protein provides the hormone with protection from degrada-tive enzymes. However, in the tobacco homworm an esterase, able to hydrolyze the protein-bound juvenile hormone, is produced at the start of pupal differentiation.354 The exact mechanism of action of juvenile hormones has been difficult to determine. However, it affects polyamine synthesis.355 356... 

A possible involvement of polyamines in the response has been suggested. Prolactin stimulated ornithine decarboxylase activity in Nb2 cells [109]. A specific inhibitor of this enzyme partially blocked the actions of lactogenic hormones on Nb2 cell proliferation [110], and addition of polyamines (putrescine, spermidine or spermine) restored normal growth. However, polyamines alone had no effect on Nb2 cell proliferation, suggesting that they are not the sole or major factors involved in mediating the actions of prolactin on cell growth. 

A number of the products of the decarboxylation of amino acids shown in Table 9.2 are important as neurotransmitters and hormones, such as dopamine, noradrenaline, adrenaline, serotonin (5-hydroxytryptamine), histamine, and Y - aminobutyric acid (GABA), and as the diamines agmatine andput-rescine and the polyamines spermidine and spermine, which are involved in the regulation of DNA metabolism. The decarboxylation of phosphatidylser-ine to phosphatidylethanolamine is important in phospholipid metabolism (Section 14.2.1). 

Galston, A. W., and Kaur-Sawhney, R., 1995, Polyamines as engogenous growth regulators, in Plant Hormones Physiology, Biochemistry Molecular Biology (Davies, ed. ), Kluwer Nedierlands, publishers, pp. 158nl78. 

Leveque J, Eoucher E, Havouis R, Desury D, Grail J-Y, Mouli-noux J-P. Benefits of complete polyamine deprivation in hormone responsive and hormone resistant MCF-7 human breast adenocarcinoma in vivo. Anticancer Res. 2000 20(1A) 97-101. 

At physiological pH in plants, polyamines exist as proton-ated forms. These protonated forms bind to the negatively charged phospholipid head groups and other anionic sites in membranes and alter the stability and permeability characteristics of such membranes. Polyamines also stabilize chloro-plast thylakoid membranes and retard chlorophyll loss in senescing barley leaf tissue. Polyamines also influence membrane fluidity, affect membrane localized proton pumps, and alter plant hormone responses, perhaps by competing for... 

Of course, the most obvious agonists of regulatory functions in plants are the five well-known classes of plant hormone, lAA, GAs, CKs, ABA and ethylene. In addition, there are several newer candidates including the brassinosteroids, jas-monate and the polyamines. The hormonal status of these newer entries is still somewhat uncertain. 

The crucial role played by vitamin Bg in the nervous system and in neuroendocrinology is based on the fact that various putative neurotransmitters as well as taurine, sphingolipids, and polyamines are synthesized by pyridoxal phosphate (PLP)-dependent enzymes. There are numerous biological effects of vitamin Bg unrelated to the role of PLP as a coenzyme. PLP is an antagonist of both the voltage-mediated and the ATP-mediated calcium transport systems. PLP modulates the activities of steroid hormone receptors and transcription factors. The preventive effect of vitamin Bg on tumorigenesis might also derive from the antioxidant functions of this vitamin. 

The next four chapters address the construction of designed and native complex structures, such as polyamines (Hahn and Schepers), natural products (Mentel and Breinbauer) and peptides, with a focus on identification of bio active hormone structures (Haack and Beck-Sickinger). Fmthermore, the automated synthesis of carbohydrates is addressed in detail by Castagner and Seeberger. 

Polyamine Interactions with Plant Hormones Crosstalk at Several Levels... 

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