Protein-linked carbohydrates

Structures and Biological Functions of Protein-Linked Carbohydrates... 

The 4-phosphopantetheine group of CoA is also utilized (for essentially the same purposes) in acyl carrier proteins (ACPs) involved in fatty acid biosynthesis (see Chapter 25). In acyl carrier proteins, the 4-phosphopantetheine is covalently linked to a serine hydroxyl group. Pantothenic acid is an essential factor for the metabolism of fat, protein, and carbohydrates in the tricarboxylic acid cycle and other pathways. In view of its universal importance in metabolism, it is surprising that pantothenic acid deficiencies are not a more serious problem in humans, but this vitamin is abundant in almost all foods, so that deficiencies are rarely observed. 

Glycoproteins are widely distributed proteins— with diverse functions—that contain one or more covalently linked carbohydrate chains. 

The primary walls of growing plant cells are composed of 90% carbohydrate and 10% protein (51). Carbohydrate in the primary wall is present predominantly as cellulose, hemicellulose, and pectin. The pectic polysaccharides, are defined as a group of cell wall polymers containing a-l,4-linked D-galactosyluronic acid residues (62,76). Pectic polysaccharides are a major component of the primary cell waU of dicots (22-35%), arc abundant in gymnosperms and non-graminaceous monocots, and are present in reduced amounts (-10%) in the primary walls of the graminaceae (27,62). 

O Ketoacidosis is a dangerous condition that is characterized by the acidification of the blood and an acetone odour on the breath. The condition occurs when levels of oxaloacetic acid for the citric acid cycle are low. This leads to a buildup of acetyl CoA molecules, which the liver metabolizes to produce acidic ketone bodies. Since carbohydrates are the main source of oxaloacetic acid in the body, high-protein, low-carbohydrate diets have been linked to ketoacidosis. 

Fig. 1. The GP Ib-IX-V complex. The complex consists of seven transmembrane polypeptides denoted GP Iba (mol wt 145,000), GP Ibp (mol wt 24,000), GPIX (mol wt 17,000) and GP V (mol wt 82,000), in a stoichiometry of 2 2 2 1. The hatched region represents the plasma membrane. The area above the hatched region represents the extracellular space that below represents the cytoplasm. The complex is a major attachment site between the plasma membrane and the cytoskeleton. Two molecules associated with the cytoplasmic domain are depicted a 14-3-3 dimer, which may mediate intracellular signaling, and actin-binding protein, which connects the complex to the cortical cytoskeleton and fixes its position and influences its function. The dark circles represent O-lihked carbohydrate and the dark squares represent IV-linked carbohydrate. Both types of carbohydrate are added after...

There are three classes of macromolecule used in cellular metabolism nucleic acids, proteins and carbohydrates. All three, identified below, are covalently linked polymeric assemblages of small building blocks . 

NE is a basic protein due to the large number of arginine residues and has an isoelectric point between 10 and 11 1251. There are at least three iso-forms of NE, which can be separated by isoelectric focusing or by polyacrylamide gel electrophoresis. The istfonns have identical N-terminal sequences and similar catalvtie activity and are believed to arise from minor differences in two N-linked carbohydrate side chains. The major form contains about 22% carbohydrate. 

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