Carbohydrate hormones

The binding methods used depend on the structure of the targeting moiety. Carbohydrates, hormones, and antibodies (or their fragments) are frequently used to direct polymer conjugates to specific cell subsets. 

As complex as the regulation of carbohydrate metabolism is, it is far from the whole story of fuel metabolism. The metabolism of fats and fatty acids is very closely tied to that of carbohydrates. Hormonal signals such as insulin and changes in diet or exercise are equally important in regulating fat metabolism and integrating it with that of carbohydrates. We shall return to this overall metabolic integration in mammals in Chapter 23,... 

Biosynthetic Human Insulin from E. coli. Insulin [9004-10-8] a polypeptide hormone, stimulates anaboHc reactions for carbohydrates, proteins, and fats thereby producing a lowered blood glucose level. Porcine insulin [12584-58-6] and bovine insulin [11070-73-8] were used to treat diabetes prior to the availabiHty of human insulin [11061 -68-0]. AH three insulins are similar in amino acid sequence. EH LiHy s human insulin was approved for testing in humans in 1980 by the U.S. EDA and was placed on the market by 1982 (11,12). 

Structure—function relationships of prolactin among a variety of species have been pubUshed (17,18). Only one gene for prolactin appears to exist (19). Although classically placed in the category of simple protein hormones, prolactin can be glycosylated. Carbohydrate attachment occurs at Asn-31, where the consensus glycosylation sequence Asn—X—Ser is found. 

Fig. 3. Processing steps of rat and bovine prepro-vasopressin lea ding to the hormone vasopressin and its carrier protein, neurophysin (14). (a) Putative signal peptide (b) vasopressin (c) neurophysin (d) glycopeptide. CHO = carbohydrate.

The adrenal cortex produces steroidal hormones that are associated with carbohydrate, fat, and protein metabolism, electrolyte balance, and gonadal functions (58). One of these, cortisone [53-06-5] ( ) demonstrated a remarkable ability to relieve the symptoms of inflammatory conditions... 

The notion that complex carbohydrates eHcit a gradual, steady secretion of insulin while sugars cause a sudden release of this hormone accompanied by a rapid drop in blood glucose has fostered the behef that hypoglycemia is affected by sucrose ingestion. However, research does not support this conclusion (63). 

Storage and utilization of tissue glycogen, maintenance of blood glucose concentration, and other aspects of carbohydrate metabolism are meticulously regulated by hormones, including insulin, glucagon, epinephrine, and the glucocorticoids. 

It was known as early as 1927 that the adrenal glands of mammalian species secrete a series of substances essential to the survival of the individual. The hormonal nature of these secretions was suggested by the observation that extracts of the adrenal gland and more specifically of the outer portion of that organ (cortex) would ensure survival of animals whose adrenals had been excised. By 1943 no fewer than 28 steroids had been isolated from adrenal cortical extracts. These compounds were found to be involved in the regulation of such diverse and basic processes as electrolyte balance, carbohydrate metabolism, and resistance to trauma, to name only a few. 

Biochemistry is carbonyl chemistiy. Almost all metabolic pathways used by living organisms involve one or more of the four fundamental carbonvl-group reactions we ve seen in Chapters 19 through 23. The digestion and metabolic breakdown of all the major classes of food molecules—fats, carbohydrates, and proteins—take place by nucleophilic addition reactions, nucleophilic acyl substitutions, a substitutions, and carbonyl condensations. Similarly, hormones and other crucial biological molecules are built up from smaller precursors by these same carbonyl-group reactions. 

Lipids are naturally occurring organic molecules that have limited solubility in water and can be isolated from organisms by extraction with nonpolar organic solvents. Fats, oils, waxes, many vitamins and hormones, and most nonprotein cell-meznbrane components are examples. Note that this definition differs from the sort used for carbohydrates and proteins in that lipids are defined by a physical property (solubility) rather than by structure. Of the many kinds of lipids, we ll be concerned in this chapter only with a few triacvlglycerols, eicosanoids, terpenoids, and steroids. 

The first hormonal signal found to comply with the characteristics of both a satiety and an adiposity signal was insulin [1]. Insulin levels reflect substrate (carbohydrate) intake and stores, as they rise with blood glucose levels and fall with starvation. In addition, they may reflect the size of adipose stores, because a fatter person secretes more insulin than a lean individual in response to a given increase of blood glucose. This increased insulin secretion in obesity can be explained by the reduced insulin sensitivity of liver, muscle, and adipose tissue. Insulin is known to enter the brain, and direct administration of insulin to the brain reduces food intake. The adipostatic role of insulin is supported by the observation that mutant mice lacking the neuronal insulin receptor (NDRKO mice) develop obesity. 

Triiodothyronine (3, 5,3-L-triiodothyronine, T3) is a thyroid hormone. It is producedby outer ring deiodination of thyroxine (T4) in peripheral tissues. The biologic activity of T3 is 3-8 times higher than that of T4. T3 is 99.7% protein-bound and is effective in its free non-protein-bound form. The half-life of triiodothyronine is about 19 h. The daily tur nover of T3 is 75%. Triiodothyronine acts via nuclear receptor binding with subsequent induction of protein synthesis. Effects of thyroid hormones are apparent in almost all organ systems. They include effects on the basal metabolic rate and the metabolisms of proteins, lipids and carbohydrates. 

Insulin is a hormone manufactured by the beta cells of the pancreas. It is the principal hormone required for the proper use of glucose (carbohydrate) by the body. Insulin also controls the storage and utilization of amino acids and fatty acids. Insulin lowers blood glucose levels by inhibiting glucose production by the liver. 

The tiiyroid hormones influence every organ and tissue of tiie body. These hormones are principally concerned with increasing tiie metabolic rate of tissues, which results in increases in tiie heart and respiratory rate, body temperature, cardiac output, oxygen consumption, and the metabolism of fats, proteins, and carbohydrates. The exact mechanisms by which tiie tiiyroid hormones exert their influence 011 body organs and tissues are not well understood. 

Periodate Oxidation, Acid Hydrolysis, and Structure-Activity Relationships of Human Pituitary, Follicle-Stimulating Hormone, and Human Chorionic Gonadotrophin, J. F. Kennedy, M. F. Chaplin, and M. Stacey, Carbohydr. Res. 36 (1974) 369-377. 

Ghanges in the availability of substrates are responsible for most changes in metabolism either directly or indirectly acting via changes in hormone secretion. Three mechanisms are responsible for regulating the activity of enzymes in carbohydrate metabolism (1) changes in the rate of enzyme synthesis, (2) covalent modification by reversible phosphorylation, and (3) allosteric effects. 

In addition to fiber and carbohydrate content, protein intake from legumes may have weight-loss benefits for obese individuals just because proteins enhance post-meal satiety (Rolls, 1995). However, a possible specific role for phytoestrogens in obesity has been postulated through the modulation of the satiety response, a neuroendocrine mechanism controlled by leptin (a hormone secreted by adipose tissue and already known to be regulated by... 

Toxic compounds polychlorinated biphenyls, polycyclic aromatic hydrocarbons, organochlorine pesticides, chlorinated pesticides, dioxins, veterinary drug residues, hormone residues, aflatoxins, toxic compounds in shellfish. Compoimds of nutritional significance in foods vitamins, fat, lipids, carbohydrates, protein, energy-calorific value, proximates, dietary fibre, ash. Other compounds hormones in blood serum... 

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