Abstract
In Chapter I is a general description of novel metal complexes which hydrolytically cleave peptides, proteins, DNA, and other biological molecules. These reagents are becoming the more important as potential therapeutic agents. A panel of ligands was investigated for coordination to ZrIV and other metals in groups 4, 5, and 6 to effect the greatest degree of hydrolysis. Chapter II describes a ZrIV complex which is capable of hydrolyzing a 30 amino acid peptide, insulin chain B, with amino acid specificity. Oxidized insulin chain B peptide was hydrolyzed after only 4 h of treatment at pH 7.0 and 60 °C using ZrCl4 in the presence of 4,13-diaza-18-crown-6. MALDI-TOF and ESI LC-MS mass spectra indicated that insulin chain B was hydrolyzed by ZrIV at the Gly8-Ser9, Ser9-His10, and Gly20-Glu21 amide bonds within the oligopeptide. To our surprise, the cysteine sulfonic acid sequences Cys(SO3H)7-Gly8 and Cys(SO3H)19-Gly20 were also cleaved. To the best of our knowledge, this constitutes the first example of metal-assisted hydrolysis of a Cys(SO3H)-Xaa amide bond. This is significant in light of the fact that cysteine sulfonic acid formation in proteins is triggered by oxidative stress and has been associated with amyloid fibril formation, Parkinson’s disease, and other deleterious, physiological processes.
Chapter III describes the metal-assisted hydrolysis of sphingomyelin which is a principle phospholipid component of animal cell membranes. The sphingomyelin assays showed evidence of metal-assisted hydrolysis after 20 h of treatment at lysosomal pH 4.8 and cytosolic pH 7.0 at both physiological temperature 37 °C and 60 °C. The metal ion CeIV was the most reactive, followed by ZrIV, and then HfIV. The goal of this work is to develop metal-based reagents to reverse the lethal build-up of sphingomyelin that occurs in lysosomes of patients suffering from Niemann-Pick disease.
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