A Major Common Trisulfated Hexasaccharide Core Sequence, Hexuronic Acid(2-Sulfate)-Glucosamine(N-Sulfate)-Iduronic Acid-N-Acetylglucosamine-Glucuronic Acid-Glucosamine(N-Sulfate), Isolated from the Low Sulfated Irregular Region of Porcine Intestinal Heparin*