A new kinetic model for the accumulation of poly(3‐hydroxybutyrate) in alcaligenes eutrophus, 1. Granule growth

Abstract

A new kinetic model is proposed for the accumulation of poly(3‐hydroxybutyrate) (PHB) in Alcaligenes eutrophus. The model developed is closely related to the descriptive model of Harkins for the emulsion polymerization process. The PHB accumulation is discussed in terms of polymerization events such as initiation, propagation and termination, taking into account the heterogeneous nature of the system. Experimental results on the PHB accumulation in Alcaligenes eutrophus can be described in both a quantitative and qualitative manner by the model. Further, it is shown that the decrease in the rate of polymerization during the PHB accumulation can be explained by coalescence of the granules. The decrease of the molecular weight of the polymer formed during the accumulation process can be fully explained in terms of the kinetic mechanisms of progapation and chain transfer, and the effect of granule size on these.

Isolation and Structure Determination of Complexed Poly(3‐hydroxyalkanoate) from Beet (Beta vulgaris L.)

“…The pathway of sPHB biosynthesis from acetyl‐CoA is well established with the bacterium Ralstonia eutropha 29–32. The kinetic investigation of in vivo sPHB biosynthesis has led to the prosposal of polymerization mechanisms of the ( R )‐3‐HB‐CoA substrate involving the three stages of initiation, propagation, and termination 33,34. In turn, Anderson et al35 found the presence of sPHB, masked at the hydroxyl end group, in Ralstonia eutroph .…”

Growth and kinetics ofin vitro poly([R]-(-)-3-hydroxybutyrate) granules interpreted as particulate polymerization with coalescence

“…Such high molecular weights are remarkable for a polycondensation polymerization. The growth time required to form a propagating polymer-synthase conjugate is approximately 15 min 18) , which is small compared to the total polymerization time of about 6 000 min for in vivo polymerization. In the in vitro reaction this growth time (i. e. 15 min) is a significant portion of the total reaction time (i. e. 120 min).…”

“…A second assumption is that the by-product of the reaction, CoA does not inhibit the enzyme as is true for the in vivo biosynthesis 12) although CoA may act as a chain transfer agent 18) . A comparison of the values of V max and K M for the in vivo and in vitro systems (Tab.…”

“…De Koning and Maxwell 17) compared PHB biosynthesis to emulsion polymerization. Their model was expanded by Kurja et al [18][19][20] to include the heterogeneity of the biosynthesis. In this paper we report direct visualization of the in vitro PHB granule growth by TEM and Cryo-TEM.…”

Emulsion Polymerization

“…Very recently, De Koning and Maxwell (1.993) drew an analogy between the conventional emulsion polymerization process and the biosynthesis of PHAs. Based on this, Kurja et al (1994Kurja et al ( ,1995 made a more quantitative description of the accumulation of poly-(/? )-3-hydroxybutyrate (PHB) in Alcaligenes eutrophus.…”