Permeation and stereospecificity of hydrolysis of peptide esters within intact lysosomes in vitro

Various dialanine ethyl esters and di- and trimethionine methyl ester diastereomers have been shown to bring about, at a concentration range of 0.5 5mM, the loss of latency of rat liver by lysosomal acid phosphatase. Concurrently an examination was made of the hydrolysis of the peptide esters by a lysosomal enzyme composite.The total hydrolysis of peptide esters involves several steps. Using a variety of siastereomers it was possible to elucidate the stereospecificity of the enzymes involved, i.e. an ester bond involving a D-amino acid residue as well as peptide bonds involving either a DD or a DL configuration in the amino terminal end and an LD configuration in a sequence of DLD are not susceptible to enzymic hydrolysis.A correlation was found between the potency of a given peptide ester in damaging lysosomal integrity and its susceptibility to hydrolysis by the lysosomal enzyme composite. It is suggested that lysosomal rupture stems from intralysosomal peptide ester hydrolysis, leading to an accumulation of zwitteron degradation products. The broad stereospecificity of the permeating species and the discrimination between trialanine and trimethionine esters lead to the suggestion that the permeation involves partition between the medium and the non-polar regions of the lysosomal membrane.