... ma intained by two s ystems. One is de novosynthesis from b uilding blocks, glutamate, cysteine, and glycine, via two ATP-con suming s teps involving c-g lut-amylcysteine synthetase ( cGCS) and ... in both arginine and cysteine. The cysteinesulfhydryls in protamine must form disulfide bond topackage DNA into small sperm head during the maturationprocess. Thus, while cysteine, a building ... meas-uring its enzymatic activity and examining the geneexpression and localization of the protein. Levels of GRactivity, the protein, and the corresponding mRNA werethe highest in epididymis...