Photoöxidation of crystalline lysozyme in the presence of methylene blue and its relation to enzymatic activity

The Roles of Imidazole in Biological Systems

“…For lysozyme, iodination (83), and plioto-oxidation (203) have heen used ; low activity heems poshihle n-it,hout histidine ('203). C.…”

Quantum Yield Studies of the Photodynamic Inactivation of Trypsin

“…Photodynamic oxidation of histidine and other amino acids has been shown to occur (9-11). Weil et al (79)(80)(81), have been able to correlate the less of enzymatic activity with the photeoxidation of these amino acids in such enzymes as lysozyme, chymotrypsin and ribenuclease, presumably because the photooxidation alters the active site. This has been done more recently with lactic dehydrogenase (82).…”

A Possible Role for Arginine in Enzyme Mechanisms

“…In our opinion, the data do not necessarily support this relationship, especially, for example, in the case of lysozyme where 30 per cent of the activity was retained even after all of its histidine was oxidized. 2 To the above should also be added the more direct evidence derived from the elegant experiments of Barnard and Stein, which appears to demonstrate the essential role of histidine in the activity of ribonuclease. 3 The evidence cited lends support to the hypothesis that histidine participates in at least some enzyme mechanisms.…”

“…The acylated guanido group therefore has two interesting properties: (1) It can be acylated to yield a derivative that deacylates under mild conditions; (2) It is less basic than the free guanido group, having a pK near neutrality. Both properties are possessed by the imidazole nucleus of histidine.…”