Ethylene binding

Schaller, G.E. Bleecker, A.B. Ethylene-binding sites generated in yeast expressing the Arabidopsis ETRl gene. Science, 270, 1809-1811 (1995)... 

Although apparently derived from the bacterial two-component signaling system, the ethylene system in Arabidopsis is different in that the His kinase activity that defines component 1 in bacteria is not essential to the transduction in Arabidopsis. The genome of the cyanobacterium Anabaena encodes proteins with both an ethylene-binding domain and an active His kinase domain. It seems likely that in the course of evolution, the ethylene receptor of vascular plants was derived from that of a cyanobacterial endosymbiont, and that the bacterial His kinase became a Ser/Thr kinase in the plant. 

In attempting to model the MJ/ethylene system, we view a two-step process MJ absorption in the membrane is directly related to MJ concentration, but its interaction with one or more of the ethylene binding proteins is effective only at higher concentrations. Hence, at low to high MJ concentrations, the modulat-... 

The matrix isolation experiments using epr, ir, uv-visible and other spectroscopic techniques on transition metal-olefin complexes [8,49] have naturally attracted the attention of theoretical chemists and calculations on the Ni-C2H4 system were reported in one of the first theoretical-experimental papers mentioned in the introduction [16]. These results were later supplemented with a larger (double-zeta) basis set [3Q] and also [31] extended for a Ni(C2H4)2 system. The main conclusions are that a net charge transfer of almost 1/5 of an electron from the metal to the ethylene is evident and that a donation and back donation mechanism consistent with a classical Dewar-Chatt-Duncanson model exists. The Ni-ethylene binding energy is 12.8 kcal/mol. 

It now appears generally accepted that a metal [52], perhaps Cu(I), [53,54] is involved in ethylene binding. The Ag" ion speciflcally inhibits the action of ethylene [55] and inhibits ethylene binding both in vitro [56] and in vivo [57], which lends weight to the metal-complex hypothesis. 

A major advance in this area was the development of techniques to measure ethylene binding in vivo [16], which are unique among plant growth regulators. These techniques were later modified to take into account effects of ethylene metabolism and endogenous ethylene production [11,17]. 

Fig. 1. Association and dissociation plots for ethylene binding to 6-day-old pea epicotyls. The association plot ( ) was produced by incubating 10 g F.W. of pea epicotyls in 40 nl P C-ethylene 20 p.1 P C-ethylene for various time intervals. The dissociation plots were produced by incubation in 31 or 34 nl P C-ethylene 20 pi P C-ethylene for 1 ( ) or 20 ( ) hours, respectively, before the introduction of 20 pi P C-ethylene (indicated by arrows). Binding of C-ethylene was then measured after various time intervals. Adapted from Sanders et al. [21].

Fig. 2. Scatchard plots for C-ethylene binding to 6-day-old pea epicotyls in which ethylene production was suppressed. Fast associating sites (O) slow associating sites ( ). Adapted from Sanders et al. [21].

A comparison of the effects of ethylene analogues and other substances upon ethylene binding and growth of pea... 

Concentration of ethylene-binding Number of ethylene-binding sites per sites, pmol g FW cell (x 10 )... 

A further prominent band at 50 kDa recognised only by HRR corresponds to a band detected if partially purified Phaseolus membrane proteins are screened with antibodies raised to the 28 and 26 kDa proteins noted above. It seems likely therefore that the Phaseolus ethylene binding protein is homologous to ETRl, ERS and NR. 

By far the most exciting development of this work was the demonstration by Schaller and Bleecker [31] that transformation of yeast with the wild type ETR gene conferred the ability to bind ethylene in a saturable and reversible manner and with an appropriate Kp (2.4xl0 M). These results taken together with those outlined above provide almost conclusive evidence that the ETR gene product is indeed an ethylene receptor. In the same work expression of truncated forms of ETRI in yeast provided further evidence that the N-terminal hydrophobic domain of the protein is the site of ethylene binding. 

Novikova et al. [26] and Raz and Fluhr [44] both showed that ethylene was capable of promoting protein phosphorylation in peas and tobacco respectively. In the former work immunoprecipitation with antibodies raised to the 26 and 28 kDa ethylene-binding bands from Phaseolus referred to in section 2.1 indicated that phosphorylation of these components was promoted by ethylene. In the work of Raz and Fluhr [44], protein phosphorylation was blocked by protein kinase inhibitors and enhanced by okadaic acid... 

The trends in metal ion-ethylene binding energies in Table 5 can be analysed as functions of basis set, theoretical level and metal ion. In contrast to the proton affinity calculation described above where zero-point energy difference contributed more than 6 kcalmoP to the final binding energy (BE) value, the vibrational frequencies in Table 7 show that the electronic energy part of the complex coordination energy will be reduced only by about... 

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