Glycogenic amino acids

VITAMIN Be IS IMPORTANT IN AMINO ACID GLYCOGEN METABOLISM IN STEROID HORMONE ACTION... 

In vitro, GH has many effects on adipose tissue and cells, including stimulation of lipolysis and actions on glucose utilization [89,90]. Short-term effects in vitro are mainly insulin-like (increased utilization of glucose and amino acids, glycogen synthesis, antilipolytic actions, etc.) and may be mediated by mechanisms similar to those of insulin, including dephosphorylation of hormone-sensitive lipase [91]. In the longer term adipose tissue and cells in vitro become refractory to the insulinlike effects of GH, and counter-insulin effects predominate and reflect the main actions seen in vivo. Receptors for GH have been identified in adipose tissue [90,92]. 

Vitamin Bg consists of pyridoxine (PN) and five related compounds, namely pyridoxal (PL), pyridoxamine (PM) and their respective 5 -phosphates (PEP, PNP and PMP). PLP is the major form in the human body (Figure 42.1). Vitamin Bg functions as a coenzyme in more than 100 enzymatic reactions involved in the metabolism of amino acids, glycogen and sphingoid bases. 

John.son, L. N., and Barford, D., 1994. Electro.static effects in die control of glycogen pho.sphoryla.se by pho.sphorylation. Protein Science 3 1726-1730. Di.scn.s.sion of die pho.sphate group s ability to deliver two negative charges to a protein, a property that no amino acid side chain can provide. 

The other example presented of a non-scrambled distribution of isotopes involves the synthesis of collagen. For a mature animal at steady state, we might expect extensive atomic scrambling in the sense that most of the non-essential amino acid content of this protein (78% of its carbon atoms) can be synthesized from the general pool of glycogenic substrates that arise from metabolism of all sugars and fats, although the pathway from fats is restricted... 

Nucleophilic attack by water generally results in the cleavage of the amide, glycoside, or ester bonds that hold biopolymers together. This process is termed hydrolysis. Conversely, when monomer units are joined together to form biopolymers such as proteins or glycogen, water is a product, as shown below for the formation of a peptide bond between two amino acids. 

Skeletal muscle utilizes glucose as a fuel, forming both lactate and CO2. It stores glycogen as a fuel for its use in muscular contraction and synthesizes muscle protein from plasma amino acids. Muscle accounts for approximately 50% of body mass and consequently represents a considerable store of protein that can be drawn upon to supply amino acids for gluconeogenesis in starvation. 

Gluconeogenesis is the process of converting noncarbohydrates to glucose or glycogen. It is of particular importance when carbohydrate is not available from the diet. Significant substrates are amino acids, lactate, glycerol, and propionate. 

Be Pyridoxine, pyridoxal, pyridoxamine Coenzyme in transamination and decarboxylation of amino acids and glycogen phosphorylase role in steroid hormone action Disorders of amino acid metabolism, convulsions... 

Six compounds have vitamin Bg activity (Figure 45-12) pyridoxine, pyridoxal, pyridoxamine, and their b -phosphates. The active coenzyme is pyridoxal 5 -phos-phate. Approximately 80% of the body s total vitamin Bg is present as pyridoxal phosphate in muscle, mostly associated with glycogen phosphorylase. This is not available in Bg deficiency but is released in starvation, when glycogen reserves become depleted, and is then available, especially in liver and kidney, to meet increased requirement for gluconeogenesis from amino acids. 

Pyridoxal phosphate is a coenzyme for many enzymes involved in amino acid metabolism, especially in transamination and decarboxylation. It is also the cofactor of glycogen phosphorylase, where the phosphate group is catalytically important. In addition, vitamin Bg is important in steroid hormone action where it removes the hormone-receptor complex from DNA binding, terminating the action of the hormones. In vitamin Bg deficiency, this results in increased sensitivity to the actions of low concentrations of estrogens, androgens, cortisol, and vitamin D. 

Pantothenic acid is present in coenzyme A and acyl carrier protein, which act as carriers for acyl groups in metabolic reactions. Pyridoxine, as pyridoxal phosphate, is the coenzyme for several enzymes of amino acid metabolism, including the aminotransferases, and of glycogen phosphorylase. Biotin is the coenzyme for several carboxylase enzymes. 

Goodacre, R. Edmonds, A. N. Kell, D. B. Quantitative analysis of the pyrolysis-mass spectra of complex mixtures using artificial neural networks Application to amino acids in glycogen. J. Anal. Appl. Pyrolysis 1993, 26, 93-114. 

Storage pathways are off degradative pathways are on. Glycogen has been depleted, and maintaining glucose levels becomes a big problem. AA = amino acids KB = ketone bodies ALA = alanine LAC = lactate. 

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