The type of linker, "cleavable" or "noncleavable", lends specific properties to the cytotoxic drug. Linkers are based on chemical motifs including disulfides, hydrazones or peptides (cleavable), or thioethers (noncleavable). Cleavable and noncleavable linkers were proved to be safe in preclinical and clinical trials. The mineral occurs as cleavable masses; cleavage fragments are nearly perfectly rhombohedral in shape. The main difference was the incorporation of cleavable ester groups intended to accelerate its biodegradation. It is cleavable by cathepsin and safe for therapy. Proteins targeted to the envelope of chloroplasts usually lack cleavable sorting sequence. Not all chloroplast proteins include a N-terminal cleavable transit peptide though. Three major types of linkers are flexible, rigid, and in vivo cleavable. Compared to the cleavable ester bond in a tyrosyl-tRNA, puromycin has a non-hydrolysable amide bond. Cleavable detergents are mainly used in sample preparations for mass spectrometry. Cleavable detergents are detergents that are cleaved after digestion, often under acidic conditions. In contrast, "cleavable linkers" are detached by enzymes in the cancer cell.