Pigmentation and enzymic inhibition by carbonyl compounds in the rabbit lens

Abstract

When certain α-hydroxycarbonyl or dicarbonyl compounds were added to cultured rabbit lenses, changes occurred in enzymic activity, color and fluorescence. These changes resemble the decreased metabolism and the development of color and fluorescence that is seen in some aged human lenses. One representative compound, glycolaldehyde, inhibited activity of at least one enzyme (aldolase). When added to lysine, to muscle aldolase, to dialyzed lens homogenates or to intact cultured rabbit lenses, glycolaldehyde elicited u.v.-fluorescence and color, the latter ranging progressively from yellow to brown or even to black. Glycolaldehyde in solution with lysine at pH 8 formed a 1-1 adduct. Through subsequent reactions of the Maillard type there occurred further changes yielding a progression of color similar to that seen in glycolaldehyde-treated lenses or in colored human lenses. Other a-hydroxycarbonyl compounds or dicarbonyls which are inhibitory to metabolism in the lens (T. G. Scharff and O. L. Montgomery, Proc. Soc. exp. Biol. Med. 134, 658 1970) also probably underwent Maillard-type reactions with amino acids in solution to form similarly colored, fluorescent products with muscle aldolase, dialyzed lens homogenates or intact lenses. It is possible that colored Maillard-type complexes between unidentified carbonyl compounds and free or protein-incorporated amino acids may be involved in reduced metabolism and in color development in the aged human lens or other pigmented, aging tissues.