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Enhancement of Sulfhydryl Group Availability in the Intestinal Brush Border Membrane by Deficiencies of Dietary Calcium and Phosphorus in Chicks

Department of Physiology, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

The reactivity and availability of sulfhydryl (-SH) groups in brush border membranes (BBM) from chicks adapted to a calcium-deficient (low Ca) or a phosphorus-deficient (low P) diet were determined. The calbindin-D_28K concentrations of the intestinal mucosa of the low Ca and low P groups were both increased 2.5-fold, demonstrating that adaptation to the mineral deficiencies had occurred. By the Ellman reaction, a threefold increment in -SH groups in BBM from both mineral-deficient groups was noted. By using DACM (N-7-dimethylamino-4-methylcoumarin-3-yl maleimide), a fluorescent probe for -SH groups, it was observed that fluorescence development was considerably greater with BBM from the low Ca and low P groups than with BBM from the controls, whether measured in the absence of presence of sodium dodecyl sulfate (SDS). In the absence of SDS, the pseudo-first-order reaction rate constants, k', calculated from the fluorescence data, were greater than the control group values, but in the presence of SDS, the k' values for all groups were about the same. Similar changes in BBM-SH groups were previously observed when 1,25-dihydroxycholecalciferol was given to vitamin D-deficient chicks. The redox state of the sulfhydryl groups in enzymes and transport proteins is known to affect the level of their activity. The functional significance of the present observations concerning the -SH groups of chick intestinal BBM, particularly in relation to vitamin D-dependent calcium and phosphorus absorption, is not known but is under investigation.

KEY WORDS: • chicken • intestine • brush border membranes • sulfhydryl groups • calcium deficiency • phosphorus deficiency

¹ Permanent address: Department of Biochemistry, Faculty of Medicine, National University of Cordoba, Cordoba, Argentina.

² Present address: Department of Nutrition, University of Kuopio, Kuopio, Finland.

Manuscript received 5 December 1989. Revision accepted 27 April 1990.