Tubular organization of crystalline argininosuccinase

摘要: Abstract 1. 1.|Argininosuccinase ( l -argininosuccinate arginine-lyase, EC 4.3.2.1) from bovine liver crystallizes in the form of fine needles. When viewed by electron microscopy these are seen to be paracrystals, each needle consisting a spindle-shaped bundle loosely packed, hollow tubules. The tubules have uniform width 210 A and wall thickness 65 A. set helices (Set 1), placed almost perpendicularly long axis having periodicity 50 is clearly resolved whole mount preparations. 2. 2.|Optical diffraction analysis indicates that repeat units tubular walls arranged single basic helix probably has about 3.5 per turn (see next paper 1 ). Independent physical data shown enzymatically active dimer two similar subunits. Calculations based on indicate tubule can identified with enzyme. 3. 3.|Electron microscope images samples collected during early stages formation paracrystals suggest sequence self assembly Tubule begins linear aggregation enzyme molecules into short, irregular ribbon-like sheets, one molecular layer thickness; elongate close over which become grouped packed bundles.