text: β-Hydroxybutyric acid is the precursor to polyesters, which are biodegradable plastics. This polymer, poly(3-hydroxybutyrate), is also naturally produced by the bacteria Alcaligenes eutrophus.
  β-Hydroxybutyrate can be extracted from poly(3-hydroxybutyrate) by acid hydrolysis.
  The concentration of  in blood plasma is measured through a test that uses β-hydroxybutyrate dehydrogenase, with NAD as an electron-accepting cofactor. The conversion of  to acetoacetate, which is catalyzed by this enzyme, reduces the NAD to NADH, generating an electrical change; the magnitude of this change can then be used to extrapolate the amount of  in the sample.