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Protein Digestion and Amino Acid Absorption in the Cayman¹

Department of Biochemistry and Pharmacology, Louisiana State University Medical Center, New Orleans, Louisiana 70112

Small caymans were force-fed 10 g of raw fish muscle/100 g body weight. At intervals for the next 4 days, groups were killed and the free amino acids of the gut contents were determined. Undigested protein was hydrolyzed and the liberated amino acids were estimated. Free amino acids of the body fluids were also determined. Individual free amino acid concentrations in the gut lumen averaged below 1 mmole/liter and several were less concentrated in the lumen than in the body fluids. All amino acids were absorbed from the digested protein at about the same rate in terms of percentage of the total in the food. Feeding produced great increases in body free alanine, glycine, glutamine and lysine (tentative identification) and small increases in the others. The rate of free amino acid absorption after feeding was compared to the rate of absorption of single crystalline amino acids administered orally to caymans and alligators. Where absorption of all amino acids was rapid from the very dilute food digest, absorption of concentrated single amino acids from the gut was slow considering the concentration, and ornithine, arginine, aspartic acid and lysine were only partially absorbed. Those that were absorbed produced body fluid concentrations averaging 60 times as high as those reached when equivalent amounts were given incorporated in protein.

Manuscript received 28 January 1970.