Lysins are members of EC 3.4.24, a group of zinc-dependent metalloendopeptidases that cleave internal peptide bonds in proteins, including collagenases, thermolysins and autolysins. Thermolysin, a heat-stable bacterial protease, is used in food biotechnology to produce flavour-enhancing protein hydrolysates and in the enzymatic synthesis of the sweetener aspartame, where its specificity is exploited. Collagenases break down connective tissue and are relevant to meat tenderisation, while bacterial autolysins — enzymes that lyse the producer’s own cell walls — influence starter-culture behaviour, phage sensitivity and enzyme release during cheese ripening. Their metal dependence makes them sensitive to chelators and pH.