Basic groups, carbohydrates

Besides his fundamental research in the carbohydrate field, the functions of Courtois as the head of a hospital laboratory for many years led him to publish a number of papers dealing with clinical chemistry, among which may be cited determination of ethyl alcohol, proteins, acidic phosphatases, and trehalase in blood determination of the basic groups of proteins by phytic acid study of the phytosoluble glycoproteins in biological fluids and identification and determination of scyllitol in urine. Under the aegis of the International Pharmaceutical Federation, he participated in the standardization of the methods proposed for the assay of such enzymes as cellulases and hemicellulases. 

Fetuin is a glycoprotein which has titratable groups associated with its carbohydrate moiety (sialic acid) in addition to those present on the protein. Spiro (1960) has determined the titration curve of the native protein, as well as that of a preparation from which sialic acid had been removed. The group count differed only in the number of groups assignable to sialic acid. In particular, the value of S was the same for both proteins. It is clear from these results that the combination of sialic acid with the protein does not involve any of the basic groups of the protein. 

Fats and carbohydrates are metabolized down to carbon dioxide via an acetyl unit, CH3C=0, which is attached to a coenzyme, HSCoA, as a thioester called acetyl CoA. Acetyl CoA enters the citric acid cycle and eventually is converted to two molecules of carbon dioxide. The first step in the citric acid cycle is the aldol of acetyl CoA with oxaloacetate (Fig. 8.6). What is so elegant about this aldol is that the acidic and basic groups within the enzyme s active site provide a route that avoids any strongly acidic or basic intermediates. The enzyme accomplishes an aldol reaction at neutral pH, without an acidic protonated carbonyl or basic enolate intermediate via push-pull catalysis (Section 7.4.3). 

Starch is a condensation polymer made up of hundreds of glucose monomers, which split out water molecules as they chemically combine. Starch is a member of the basic food group carbohydrates and is found in cereal grains and potatoes. It is also referred to as a polysaccharide, because it is a polymer of the monosaccharide glucose. Starch molecules include two types of glucose polymers, amylose and amylopectin, the latter being the major starch component in most plants, making up about three-fourths of... 

The nature of the union between a dye and a fabric is still an open question. It is probable that in certain cases chemical compounds are formed, and that in others the fabric forms with the dye a solid solution, or holds it mechanically within its fibers as the result of adsorbtion. The fact that many colored substances which contain weakly acidic or basic groups dye wool and silk but do not dye cotton is evidence that the fixing of the dye in the animal fiber is probably the result of chemical action. Wool and silk are proteins and cotton is a carbohydrate. The proteins form compounds with weak acids and bases, whereas cotton, which is cellulose reacts only with the strongest acids and bases. Cotton can be dyed by some organic compounds, however,—a fact which leads to the view that in certain cases the union of the dye and the fabric is of a physical nature. 

Many lipids and carbohydrates may contain acidic or basic groups, so their charges may also depend on the pH. 

The olefinic substrates employed in carbohydrate synthesis can be roughly divided into three basic groups comprising alcohols, aldehydes or hydroxyalde-hydes, and hydroxy acids or lactones. 

The basic carbohydrate molecule possesses an aldehyde or ketone group and a hydroxyl group on every carbon atom except the one involved in the carbonyl group. As a result, carbohydrates are defined as aldehyde or ketone derivatives of polyhydroxy alcohols and their reaction products. A look at the formula for glucose shows that it contains hydrogen and oxygen atoms in the ratio in which they are found in water. The name carbohydrate... 

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