Effect of dietary sucrose on synthesis and degradation of intestinal sucrase.

Rates of synthesis and degradation of sucrase-isomaltase were measured along the crypt-villus unit of intestinal mucosa of rats fed either a high-sucrose or a carbohydrate-free diet. The objective of the study was to investigate i) the biochemical basis for the accumulation of sucrase during migration and differentiation of the enterocyte, leading to changes in distribution of activity of sucrase along the villus, and ii) the mechanism for the adaptation of sucrase activity to the amount of dietary carbohydrate. The results indicate that synthesis of sucrase is more rapid than degradation at the crypt-villus junction and in the lower part of the villus, producing a progressive accumulation of enzyme. The decreased activity at the tip of the villus is the consequence of a decided diminution of synthesis while the rate of degradation remains elevated. In rats fed a diet high in sucrose, the increased activity (3.25 times) is associated with much more rapid synthesis (2.6 times), while degradation is only slightly slower (0.8 times) than in those animals deprived of carbohydrate.