The Effect of Pyridoxine Deficiency on Aortic Elastin Biosynthesis

Abstract

An intake of dietary copper is required for the formation of desmosine and isodesmosine, the important cross-linking amino acids of elastin (1, 2). These cross-linking units arise as the result of an oxidation of lysine, at its ∊-amino group, to α-aminoadipic semialdehyde, a step catalyzed by a copper-containing amine oxidase (3). Hill and Kim (4) suggested that this enzyme contains a pyridoxine derivative and that pyridoxine deficiency affects elastin biosynthesis in the same manner as does copper deficiency. However, information gathered in recent experiments in this laboratory was not in agreement with some of the data reported by these investigators. We decided to explore the problem by comparing quantitatively the desmosine and isodesmosine content of aortic elastin in pyridoxine-deficient and in control chicks and, with the aid of an in vitro ¹⁴C-lysine pulse-labeling technique, the degree of oxidation of lysine, at its ∊-amino function, in pyridoxine-deficient and in normal chick aortas.

Our results, in general, confirm the hypothesis of pyridoxine involvement in elastin biosynthesis. Discordance remains, however, between the data reported here and those reported by Hill and Kim (4) with respect to some corollary aspects.

Methods. Feeding studies were conducted with day-old Arbor Acre chicks fed a basal dried skim-milk diet, with or without copper supplement (5); or a vitamin-free casein diet (4), supplemented with all vitamins except for individual deficiencies in riboflavin, pyridoxine, and pantothenic acid. All groups were fed ad libitum, with the exception that a fully supplemented control group was pair fed to the pyridoxine-deficient group. After 14 days on the experimental diets, the chicks were killed, their aortas were removed and the elastin content therein was determined as described previously (5). Extraction time in 0.1 N NaOH was reduced to 60 min at 100°, a period previously shown to be sufficient to remove collagen and other protein (6).