Chapter 13 Molecular Modification of Renal Brush Border Maltase with Age: Monoclonal Antibody-Specific Forms of the Enzyme

Abstract

Publisher Summary This chapter discusses the molecular modification of renal brush border maltase with age. Maltase (α-D-glucoside glucohydrolase) is the major disaccharidase in rat renal brush border membranes. Maltase-specific activities in renal cortex homogenates and brush border membranes prepared from senescent 24-month-old rats are decreased 30–40% relative to the activities of the enzyme from 6-month-old mature adults. This decrement is not attributable to a change in the affinity of the enzyme for substrate, a difference in the stability of the enzyme in homogenates, or the presence of an activator in the young or an inhibitor in the aged. The chapter discusses whether the decrease in the membrane-bound maltase activity with age results from an alteration in the enzyme protein per se or from a change in the enzyme's membrane environment, which is reflected secondarily as a loss in enzyme activity. The results exhibit that the antigenicity of renal brush border membrane maltase is altered during the aging process. These findings indicate that young and old maltase has different epitopes and, thus, the data are consistent with and may reflect the age-dependent conformational change of the enzyme, suggested by the alteration in its circular dichroism spectrum.