8 THE ROLE OF ALGAE AND PLANKTON IN MEDICINE 



mannitol anhydride), dulcitol and sorbitol (mannitol isomers), and flori- 

 doside (a glycerol-D-galactoside) all occur in various species of Rhodo- 

 phyceae. Trehalose, a glucopyranoside, is present only in fresh water 

 species of Rhodophyceae. The chief intracellular reserve products in many 

 species are glucose polymers. Thus floridean starch is characteristic of the 

 Rhodophyceae; it is composed exclusively of glucose residues, but differs 

 from ordinary starch in containing a large proportion of 1:3 linkages 

 and in being able to resist the effect of /^-amylase. The Phaeophyceae lack 

 starch and allied substances. Laminarin, another glucose polymer found 

 in some Phaeophyceae, comprises up to 25 per cent of the plant on a 

 dry weight basis. 



Cellulose is the main cell wall component in the Phaeophyceae and 

 Rhodophyceae, and it makes up from 2 L o 1 5 per cent of their dry weight. 

 By chemical and radiological examination, it appears to be similar to the 

 cellulose of higher plants. Other related carbohydrate substances in algae 

 include chitin, pectin, and hemicellulose. Algin, a characteristic intra- 

 cellular substance of the Phaeophyceae, forms about 25 per cent of the 

 seaweed on a dried basis. It is a calcium-magnesium salt of alginic acid, 

 a polymer of /?-D-mannuronic acid. Xylan, a polysaccharide from which 

 xylose is derived by hydrolysis, has been found in Rhodymenia palmata. 

 Other intracellular polysaccharides, composed of residues esterified by 

 sulfuric acid, include agar-agar, carragheenin, and fucoidin. 



Relatively little is known about the protein components of macro- 

 scopic algae, except that they are present in only small quantity and that 

 they are minimally assimilable by human beings. According to Cameron, 55 

 analyses indicated 6.85 per cent protein in Gelidium corneum, and 5.49 

 to 5.82 per cent in various species of Laminaria. Analyses of various kelp 

 meals and feeds for animals (who may utilize contained proteids better 

 than humans) indicated levels of 7.04, 13.12, and 5.60 per cent, re- 

 spectively. At the 1952 International Seaweed Symposium, 56 the Youngs 

 indicated that the proteins and peptides were difficult to extract from 

 algae, with only 50 per cent being obtained even by strong alkali. The 

 nitrogen of various common brown seaweeds consisted of volatile base 

 nitrogen, nitrate nitrogen, and residual Kjeldahl nitrogen. E. T. Young 

 also stated that the ^-amino-nitrogen after hydrolysis was always lower 

 than the residual Kjeldahl nitrogen because of amino-acid decomposition. 

 The amino-acids found on acid hydrolysis of Laminaria saccharina and 

 Alaria nodosum included glycine, alanine, valine, leucine, aspartic acid, 

 serine, glutamic acid, threonine, proline, phenylalanine, lysine, and argin- 



