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Sulfhydryl-Disulfide Mechanisms In Plant And Animal Perceptions
Most, if not all, common chemical messengers between insects and plants, and between them and their environments
(Rodriguez and Levin 1976, Neupane and Norris 1992, Norris and Liu 1992, Raina et al. 1992) are both elicited and perceived
by sulfhydryl / disulfide (-SH / -S-S-) -dependent mechanisms (Neupane and Norris 1992, Liu et al. 1992, Norris
1994). The energy-transduction mechanism in chemical communications by both animals and plants is sulfur dependent.
The initial studies in this area showed that 1,4-naphthoquinones serve as repellents and deterrents to Periplaneta americana
L., the American cockroach, and Scolytus multistriatus (Marsh.), the smaller European elm bark beetle, by reacting with
sulfhydryls in receptor proteins in dendritic membranes of chemosensitive neurons (Norris et al. 1970a, 1970b, 1971;
Rozental and Norris 1973, 1975; Singer et al. 1975).
The redox dependency of chemoreception in insects was also shown in studies (Norris 1969, 1970) where p-hydroquinone,
the reduced partner in the classical redox couple, p-hydroquinone / p-benzoquinone, excited feeding by S.
multistriatus; whereas, the oxidized partner, p-benzoquinone, inhibited feeding. In spite of these early findings, enthusiasm
for redox-based receptor and energy-transduction mechanisms in animal and human chemoreception has, until quite recently,
been limited. This was especially true for insect chemoreception. Although numerous research reports have confirmed that
insect chemoreception is sulfhydryl-disulfide dependent (Villet 1974; Frazier and Heitz 1975; Singer et al. 1975; Ma 1977,
1981; Vande Berg 1981), several workers in this entomological specialty (e.g., Kaissling 1971, 1974, 1987; Vogt and
Riddifbrd 1986) concluded that non-covalent bonding, but not redox reactions, are involved in the transduction mechanism in
insect chernoreception. Until recently, most researchers working in receptor and energy-transduction mechanisms in living
cells also had concluded that redox reactions were not involved. In contrast, findings by Norris (1969, 1971, 1976, 1981,
1985, 1988, 1994) have consistently indicated that redox chemistry is fundamentally involved in receptor function and
energy-transduction mechanisms. The validity of our results has been reconfirmed throughout the general field of receptors
and signal transduction (e.g., Storz et al. 1990, Van Der Vliet and Bast 1992, Stamler et al. 1992, Reichard 1993, Pyle 1993,
Ravichhandran et al. 1993). The sulfhydryl-disulfide dependent:redox chemistry of receptors and energy transduction has
become a major area of research throughout biology (Van Der Vliet and Bast 1992). Thus, these aspects of insect chemoreception
have not only been confirmed, but also are now widely viewed as a part of a much larger chemoreception 'whole'
within biology.
The Required Elemental Trait
The fundamental trait required for the evolution of a system for information generation, transfer and use in maintaining
order is the transfer of chemical groups and energy. This required trait for chemical messengers singles out phosphorus
and sulfur from all other atoms in the "Periodic System" (Wald 1969). The two basic atomic characteristics which qualify
sulfur and phosphorus uniquely as agents of chemical group and energy transfers are (a) the possession of d, in addition to s
and p, orbitals which increases their capacities to form linkages with a variety of energy potentials and (b) an intrinsic
instability of such linkages, which facilitates the exchange of chemical groups and energy (i.e., informational units) (Wald
1969). Such roles for phosphorus are well established experimentally, but they are only just now being recognized for sulfur.
However, sulfur now seems to be the most highly qualified element regarding abilities to exchange energy as information
among living forms and their abiotic environments (Wald 1969; Norris et al. 1970a, 1970b, 1971; Norris 1971, 1979,
1981, 1985, 1986, 1988, 1994; Neupane and Norris 1992; Norris and Liu 1992; Van Der Vliet and Bast 1992). First of all,
regarding such roles, sulfur, as thiol (-SH), brings to living systems a form of organic sulfur which possesses those atomic
traits which are otherwise limited to organic oxygen and are essential to organisms. However, thiol lacks most, if not all, of
those traits (or degrees thereof) possessed by oxygen which make oxygen or its free-radical derivatives, especially harmful,
even deadly to living organisms, unless the oxygen is handled in special ways, e.g., bound to hemoglobin in vertebrate blood
(Wald 1969, Harold 1986). Second, sulfur as well as phosphorus forms relatively long (i.e., loose) bonds with other atoms;
such bonds hold the attached atom less tightly and thus it may be more readily transferred, exchanged, as informational
energy in living systems (Wald 1969, Harold t986). Third, the trait which ultimately sets sulfur, as a vehicle of chemical
group and energy transfers as information, apart from phosphorus is the former's ability to form a thiol (-SH). This property
uniquely enables sulfur to readily accept, donate or variously share the basic energy unit in living systems, hydrogen (Wald
1969, Szent-Gyorgyi 1973). Thus, through sulfhydryl / disulfide (thiol, -SH / disulfide, -S-S-) redox chemistry, sulfur
uniquely brings to living cells, and their chemical communications, a "yin and yang", a give and take, mechanism for moving
hydrogens, the basic energy unit of living systems, as information between plants and animals and their abiotic environments
(Norris 1986, 1988, 1994; Neupane and Norris 1992; Norris and Liu 1992).
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