Crystal structures of a purple acid phosphatase, representing different steps of this enzyme's catalytic cycle.

Background: Purple acid phosphatases belong to the family of binuclear metallohydrolases and are involved in a multitude of biological functions, ranging from bacterial killing and bone metabolism in animals to phosphate uptake in plants. Due to its role in bone resorption purple acid phosphatase has evolved into a promising target for the development of anti-osteoporotic chemotherapeutics. The design of specific and potent inhibitors for this enzyme is aided by detailed knowledge of its reaction mechanism.

Phosphate forms an unusual tripodal complex with the Fe-Mn center of sweet potato purple acid phosphatase.

Purple acid phosphatases (PAPs) are a family of binuclear metalloenzymes that catalyze the hydrolysis of phosphoric acid esters and anhydrides. A PAP in sweet potato has a unique, strongly antiferromagnetically coupled Fe(III)-Mn(II) center and is distinguished from other PAPs by its increased catalytic efficiency for a range of activated and unactivated phosphate esters, its strict requirement for Mn(II), and the presence of a mu-oxo bridge at pH 4.90.

Extent of charge screening in aqueous polysaccharide solutions.

The absorption optical system of a Beckman XL-I ultracentrifuge has been used to monitor the Donnan distribution of ions in polysaccharide solutions dialyzed against sodium phosphate buffer (pH 6.8, I 0.08) supplemented with 0.

Limitations of the ultracentrifugal approach for measuring the effective net charge of a macroion.

Limitations have been detected in a recently published method for macroion valence determination by an ultracentrifugal procedure for quantifying the Donnan distribution of small ions in macroion solutions dialyzed against buffer supplemented with chromate as an indicator ion. The limitation reflects an implicit assumption that sedimentation velocity affords an unequivocal means of separating effects of chromate binding from those reflecting the Donnan redistribution of small ions. Although the assumed absence of significant Donnan redistribution of small ions across the sedimenting macroion boundary seemingly holds for some systems, this approximation is demonstrably invalid for others.