103. Lin, F. C., Brown, Jr. R. M., Cooper,
J., and D. Delmer. 1985. Synthesis of fibrils in vitro
by a solubulized cellulose synthase from Acetobacter xylinum.
Science 230: 822-825.
A digitonin-solubilized cellulose synthase
was prepared from Acetobacter xylinum. When this
enzyme was incubated under conditions known to lead to active
synthesis of 1,4--D-glucan polymer (cellulose), electron microscopy
revealed that clusters of fibrils were assembled within minutes.
Individual fibrils are 17 2 angstroms in diameter. Evidence
that the fibrils were freshly synthesized and cellulosic in nature
was their incorporation of the tritium from UDP-[3H]glucose
(UDP, uridine 5'-diphosphate), their binding of gold-labeled cellobiohydrolase,
and an electron diffraction pattern with 004, 200, and 012 reflections
(characteristic of cellulose synthesized in vivo) but missing
110 and 110 reflections. The small size of the fibrils is atypical
of native A. xylinum cellulose microfibrils. The fibrils
synthesized in vitro resemble, in morphology and size,
the fibrillar cellulose produced when A. xylinum is cultured
in the presence of agents that interfere with the normal process
of crystallization of the microfibrils. The solubilized enzyme
unit may therefore be producing a basic fibrillar structure that,
in vivo, interacts laterally with other fibrils to produce
native cellulose microfibrils.