NUTRITIONAL AND GENETIC APPROACHES 



the transport site. Somewhat against this view stands the high re- 

 sistance of amino acid transport in the Ehrlich ascites tumor cell 

 to inhibition by carbonyl reagents such as semicarbazide, hydroxyl- 

 amine, and aminoxyacetic acid (Christensen, 19601)). At the same 

 time, the stimulating action of the addition of 10 ~ :i to 10 ~ 4 M 

 pyridoxal or pyridoxal phosphate on amino acid transport by the 

 Ehrlich cell does not seem likely to represent merely an augmenta- 

 tion of a suboptimal carrier level (Pal and Christensen, 1961). Fur- 

 thermore, these agents seem to slow exodus more than they acceler- 

 ate entry of amino acids (Oxender, 1962b). 



Even though the action of pyridoxal at millimolar levels on 

 amino acid transport into Ehrlich cells does not represent a physio- 

 logical action, the nutritional experiments cited above show that 

 vitamin B, ; is somehow related to amino acid transport. 



Genetic approaches 



If any organism, mutant or otherwise, requires that a specific 

 carrier precursor be supplied from the environment, a special oppor- 

 tunity for identifying the carrier is presented. 



A number of genetic deficiencies of transport, especially of 

 renal transport, are known. Cystinuria has been known for a cen- 

 tury and a half. Amino acids other than cystine, including lysine 

 (Ackermann and Kutscher, 1912), were occasionally observed to 

 be excreted along with cystine. Cadaverine and putrescine were also 

 detected; these diamines may have arisen from lysine and ornithine 

 by bacterial action during the collection of urine. Full recognition, 

 however, of cystinuria as a genetically determined disease of trans- 

 port involving lysine, arginine, cystine, and ornithine is compara- 

 tively recent (Dent, 1949; Dent and Rose, 1951; Stein, 1951; Dent 

 et al, 1954). Although cystine is indeed a diamino acid, so far it 

 has not been shown in any well-defined system to use the same trans- 

 port mediator as the cationic amino acids (cf. Rosenberg et al. } 1962). 



In 1937 Kerr recognized "a different race" of sheep having high 

 red blood cell potassium levels in contrast to the majority of sheep, 

 which have low erythrocyte levels of this ion, with correspondingly 

 high sodium-ion levels. Evans (1954) showed that the same division 

 into two strains occurs in English and Scottish sheep; Evans and 

 King (1955) showed that the high-potassium character was inherited 



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