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Biochemistry, 4th Edition P59

Biochemistry, 4th Edition P59. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | 18.3 What Are the Chemical Principles and Features of the First Phase of Glycolysis 543 A DEEPER LOOK Phosphoglucoisomerase A Moonlighting Protein When someone has a day job but also works at night that is under the moon at a second job they are said to be moonlighting. Similarly a number of proteins have been found to have two or more different functions and Constance Jeffery at Brandeis University has dubbed these moonlighting proteins. Phosphoglucoisomerase catalyzes the second step of glycolysis but also moonlights as a nerve growth factor outside animal cells. In fact outside the cell this protein is known as neuroleukin NL autocrine motility factor AMF and differentiation and maturation mediator DMM . Neuroleukin is secreted by immune system T cells and promotes the survival of certain spinal neurons and sensory nerves. AMF is secreted by tumor cells and stimulates cancer cell migration. DMM causes certain leukemia cells to differentiate. How phosphoglucoisomerase is secreted by the cell for its moonlighting functions is unknown but there is evidence that the organism itself may be harmed by this secretion. Diane Mathis and Christophe Benoist at the University of Strasbourg have shown that in mice with disorders similar to rheumatoid arthritis the immune system recognizes extracellular phosphoglucoisomerase as an antigen that is a protein that is nonself. That a protein can be vital to metabolism inside the cell and also function as a growth factor and occasionally act as an antigen outside the cell is indeed remarkable. Adenylate kinase rapidly interconverts ADP ATP and AMP to maintain this equilibrium. ADP levels in cells are typically 10 of ATP levels and AMP levels are often less than 1 of the ATP concentration. Under such conditions a small net change in ATP concentration due to ATP hydrolysis results in a much larger relative increase in the AMP levels because of adenylate kinase activity. Clearly the activity of phosphofructokinase depends on both ATP