Properties of the DNA associated with crystalline yeast lactic dehydrogenase

Abstract

YLDH DNA, the polydeoxyribonucleotide associated with the crystalline enzyme yeast lactic dehydrogenase-cytochrome b 2 , has been shown to be unusual with respect to size, composition and conformation. Per enzyme particle (two heme and flavin monophosphate groups attached to a protein of mol. wt. 150,000) it consists of 33 deoxyribonucleotides: 11 deoxyadenylic, 12 deoxythymidylic, 5 deoxyguanylic and 5 deoxycytidylic. A single-stranded, yet highly ordered conformation for the DNA is suggested by measurement of its room temperature hypochromicity, thermal denaturation and renaturation, interaction with aliphatic and aromatic di-cations, formaldehyde titration and other experiments : at room temperature approximately 0·6 to 0·7 of all residues are believed to be in stacked, ordered regions, yet only 0·3 or so are actually present as hydrogen bonded base-pairs. A model involving a single-stranded “hairpin” held together by the hydrogen bonded pairs interspersed among unmatched pairs is proposed. Soluble extracts used as a source of YLDH DNA provide the source of another DNA species, relatively normal with regard to base composition and apparent conformational properties; the crystallization mother liquor yields a polyribonucleotide similar to yeast transfer RNA. These facts are considered in relation to the question of the possible artefactual nature of the YLDH DNA and the specificity of its association with the enzyme.