New aspects of rubber biosynthesis

Abstract

New aspects of rubber biosynthesis. Following a review of the site of rubber biosynthesis in Hevea brasiliensis and Parthenium argentalum, evidence is given for the initiation of polyisoprene molecules from (ranMerpenoid precursors including geranylgeranyl pyrophosphate. All franj‐14C‐geranylgeraniol has been isolated from incubations of H. brasiliensis latex serum with 14C‐isopentenyl pyrophosphate. Gel‐filtration chromatography of the serum yields very small rubber particles of high biosynthetic activity, and two proteinaceous fractions. One of these increases the biosynthesis of rubber and may contain the enzyme, isopentenyldiphosphate δ‐isomerase, whilst the other appears to inhibit rubber formation. The nature and molecular weight of the rubber formed in vitro is discussed and a mechanism for the de novo formation of rubber particles is suggested.

The separate roles of plant cis and trans prenyl transferases in cis‐1,4‐polyisoprene biosynthesis

“…2). FPP is known to be an effective initiator of rubber molecule formation (Archer and Audley, 1987;Cornish and Backhaus, 1990). Therefore, the observed stimulatory effect of the soluble trans-prenyl transferase on rubber biosynthesis can be explained without requiring a role as rubber transferase.…”

“…7). Rubber biosynthesis can occur in the absence of soluble proteins if these are substituted for by a number of different allylic diphosphate initiator molecules (Archer and Audley, 1987;Audley and Archer, 1988;Berndt, 1963;Cornish and Backhaus, 1990;Madhavan et al, 1989). Thus, it is probable that all soluble extracts reported to have rubber transferase activity (Archer et al, 1963;McMullen and McSweeney, 1966) were actually part of the rubber molecule initiation system, synthesizing essential allylic diphosphates but not cis-1,4-p0lyiso-prene.…”

“…The polymerization of the natural rubber polymer is catalyzed by the enzyme rubber transferase. Rubber transferase, a cis-prenyl transferase, requires divalent cations (such as Mg2+ or Mn2+) for activity, but rubber transferase, IPP and Mg" together will not result in rubber biosynthesis; a second substrate, an allylic diphosphate, is needed to initiate the polymerization process (Archer and Audley, 1987;Cornish and Backhaus, 1990;Madhavan et al, 1989). Hence, rubber molecule formation requires three distinct biochemical processes : (a) initiation, which requires an allylic diphosphate molecule (synthesis of allylic diphosphates is catalysed by trans-prenyl transferase enzymes) ; (b) elongation, the rubber transferase-catalyzed cis-1 ,4-polymerization …”

Seasonal Variations in Rubber Biosynthesis, 3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase, and Rubber Transferase Activities in Parthenium argentatum in the Chihuahuan Desert

“…chains catalyzed by a rubber transferase bound to rubber particles is the same in both species (Archer and Audley, 1987;Madhavan et al, 1988), but an outstanding feature of rubber formation in guayule is the stimulation of rubber biosynthesis by the exposure of the plants to low temperatures, similar to those existing in the fall and winter in the Chihuahuan Desert (Bonner, 1943;Downes and Tonnet, 1985;van Staden et al, 1986). Bonner (1943) demonstrated that the exposure of guayule plants to 27OC during the day and 7OC at night with an 8-h photoperiod for 4 months in a controlled-temperature greenhouse induced a 4-fold increase in rubber formation compared with plants grown at 27OC during the day and 27OC at night with an 8-h photoperiod.…”

Molecular Structure of Natural Rubber and Its Characteristics Based on Recent Evidence

“…However, it is difficult to ignore the possibility that FDP directly initiates polymerization, because it was reported that FDP stimulates in vitro rubber formation upon incubation with isopentenyl diphosphate (IDP) and washed rubber particles (Archer & Audley, 1987;Audley & Archer, 1988;Madhavan et al, 1989;Cornish & Backhaus, 1990). Under the same conditions, [1-3 H]neryl diphosphate was incorporated into rubber molecules (Audley & Archer, 1988).…”