Four endoglucanase temperature isoforms (T (30), T (50), T (70), and T (90)) were identified and purified from the cladodes of the xerophytic plant Opuntia vulgaris. These isoforms exhibited optimum catalytic activity at 30 A degrees C, 50 A degrees C, 70 A degrees C, and 90 A degrees C and yielded an apparent molecular mass of 150, 20, 74, and 45 kDa, respectively, on gel filtration chromatography. These isoforms were purified 24-, 25-, 29-, and 27-fold with a yield of 15%, 12%, 17%, and 19% and having a specific activity of 120, 125, 144, and 136 U/mg, respectively. The thermostable T (70) and T (90) isoforms exhibited optimum activity at pH 4.5 and 7 and also yielded a molecular weight of 66 and 36 kDa, respectively, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The T (70) had a K (m) of 43 mM and a V (max) of 12.5 mu mol min(-1) mu g(-1) of protein, and the T (90) isoform had a K (m) of 40 mM, with an apparent V (max) of 10 mu mol min(-1) mu g(-1) of protein. Western blot, immunodiffusion, and in vitro inhibition assays established the reactivity of the T (90) isoform with polyclonal anti-T (90) antibody raised in rabbit. Cross-reactivity of this antibody with the T (70) endoglucanase isoform was also noted.