Non-proteolytic Processes

While proteins are synthesized on ribosomes the translation product is often subject to considerable post-translational modification that can involve proteolytic processing of the initial proprotein and covalent modification of the processed protein by glycosylation (addition of sugar residues), acylation (e.g. with fatty acids), methylation and phosphorylation. Unconjugated proteins are those in which there is no non-amino acid substituent and conjugated proteins are those that have been modified with non-amino acid entities. 

The processes of prepropolypeptide synthesis, translocation, proteolytic processing and non-proteolytic modification can be enzymatically defined. These definitions are continuing to be developed and clarified. There are limited reports on insect neuropeptide processing (101.102. but these investigations should increase rapidly with the identification of precursor sequences via molecular genetics. The identification of processing enzymes, both proteolytic and non-proteolytic, will further open whole new areas for exploration. 

Non-solvent processes have been developed in answer to the high cost of large-scale solvent extraction. Holmes and Lim [61] described the enzymatic process used at Zeneca for the recovery of PHB and PHBV. First, a high-temperature (100 to 150 °C) treatment of the cells provokes cell lysis and denaturation of nucleic acids, which could otherwise interfere with the subsequent steps. Non-PHA biomass is then solubilized with proteolytic enzymes (pepsin, trypsin, papain, others, and mixtures thereof) and anionic surfactants. Concentration of PHA by centrifugation is finally followed by bleaching with H2O2. 

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