LDH calcutta-1: A mutation of the B subunit of human lactate dehydrogenase

The electrophoretic variant of human LDH, Calcutta-1, occurs at phenotypic frequencies of 0–4% throughout India. The variant was examined by various electrophoretic techniques and by heat stability studies. The LD₁ (B₄) isoenzyme was purified from normal and variant bloods by affinity chromatography and ion-exchange chromatography. A minimum of five Calcutta-1 LD₁ bands was demonstrated by isoelectric focusing. Electrophoresis of variant LD₁ in high-molar urea-acrylamide denaturing gels resulted in two Calcutta-1 B subunit bands, while normal gels yielded only a single band. Homozygote Calcutta-1 LDH from red cells demonstrated a decreased heat stability, while heterozygote variant LDH showed a normal heat stability. This effect was confirmed when purified LD₁'s were compared. Evidence is presented suggesting a B-subunit variant showing thermolability in the homozygous form.The author was supported by an Australian National University Scholarship.