MCAT Chemical and Physical Foundations of Biological Systems 7 — Flashcards

Questions are based on the following passage:

Arginase (RocF) hydrolyzes l-arginine to form l-ornithine and urea [CO(NH2)2]. In general, arginases have an alkaline pH optimum and require manganese for activation, but the Helicobacter pylori is optimally active with cobalt at pH 6. The metal ion forms a complex with arginine and promotes the enzymatic reaction. The arginase from Bacillus anthracis was purified for a structural and functional investigation. The B. anthracis rocF gene was cloned and expressed in E. coli. After purification, RocF was tested for arginase activity with several different metals. Arginase activity of extracts containing the expressed protein was measured at pH 6.3 and pH 9 in the presence of a wide array of metals, each individually tested at 5 mM, or using deionized water in a 'no metal' control.

Spectrophotometric readings were taken at 515 nm after 24 hours (Figure 1). A viable cell arginase assay was performed by growing B. anthracis in the absence or presence of various metal concentrations, and cells were harvested and assayed directly for arginase activity at its optimal pH (Figure 2). Finally, amino acid sequence alignment studies showed particularly high sequence conservation in a –DAHGD-residue string at the putative metal binding site.

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