GASTRIC LYSOZYME AS A DIGESTIVE ENZYME IN THE HOATZIN (OPISTHOCOMUS HOAZIN), A RUMINANT-LIKE FOLIVOROUS BIRD

The hoatzin is the only bird known to have pregastric fermentation in the crop. This digestive strategy is supported by morphological and mi crobiological adaptations analogous to those present in ruminants and ruminant-like mammals. The hoatzin expresses a lysozyme-like bacteriol ytic activity in its foregut. The enzyme has a high activity, and its low pH optimum, pepsin resistance and localization to the proventricul us allow it to be active for digestion in the stomach. The hoatzin enz yme and the ruminant gastric lysozyme present similar biochemical char acteristics. The lysis of bacterial cells may be of significance for t he nutrition of the hoatzin. We propose that the hoatzin expresses a l ysozyme which has been recruited to function as a digestive enzyme, re presenting a unique case of evolutionary convergence of digestive adap tations in this bird and foregut fermenter mammals.