Previous reports have indicated that the hexosaminidases (HEX) are tetrameric enzymes composed of either two dimers of β chains (HEX B) or a β-chain dimer and an α-chain dimer (HEX A). HEX S contains only α chains. The apparent molecular weight of both α and β chains is 25 000. We isolated and purified HEX A and B more than 6000-fold. From HEX A we prepared HEX B and a more anodically migrating HEX S, which contained only α chains. After either extensive reduction and alkylation or performic acid oxidation, HEX B gave only a single protein band in polyacrylamide gel electrophoresis in sodium dodecyl sulfate; HEX A consistently gave two bands indicating it contained chains of two different molecular weights. Other reports note two bands in HEX A but have dismissed the high molecular weight band as a dimer caused by either hydrophobic interaction or an unbroken disulfide bond. To rule out hydrophobic interaction, we determined molecular weight by gel filtration in 6 M guanidine–HC1. To ensure complete disulfide bond breakage we used a harsher reduction and alkylation procedure than previously employed by others. The results were then confirmed by the use of two performic acid oxidation techniques, the stronger method resulting in extensive peptide bond oxidation. Samples of HEX A under reduction and alkylation or the weaker performic acid oxidation procedure, again chromatographed as two approximately equal peaks (50 000 and 25 000). HEX B, and the HEX B prepared from HEX A, resulted in one 25 000-dalton peak. HEX S chromatographed as a single 50 000 peak. We conclude that either the α chain in HEX has a molecular weight of 50 000 with one α chain per α subunit or that two 25 000-dalton chains are united by a nondisulfide crosslink (e.g., an isopeptide bond).

Myelin was isolated from central white matter of beef and human brains. I t contained less than 8.1% ribonucleic acid, l e a than 8.63% deoxyribonucleic acid, and w s g l p l i p i d N-acetylneunminic acid. The preparation was 96% soluble in chioroform-methanol. Most of the insoluble materrai was sucrose. The myelin contained 19.6Y0 protein, 13.4y0 cholesterol, 86.1y0 phospholipid, and 23.6% galactslipid. A protein extracted from the rnyelin reparation with cold 0.2 N sulfuric acid gave a single sedimenting boundary in g e Spinco model E analytical ultracentrifuge. In 8 M ura-formate starch gels (pH 8.4) it migrated as a single band toward the cathode. Amino acid analysis revealed that the protein contained more than Z8Y0 dibasic amino acids, but little methisnine and no cystine. I t was rapidly hydrolyzed by trypsin. The molecular weight was estimated at 10,8W, When injected intradermally into guinea pigs, in suspension in Freund" adjuvant, it caused weight lms, a flaccid paralysis, occasional convulsions, and death, n pattern characteristic of experimental allergic encephalomyelitis. Evidence is cited for the presence of a t least one other protein in purified rnyelin.

Tay-Sachs disease is an autosomal recessive genetic disorder resulting from mutation of the HEXA gene encoding the alpha-subunit of the lysosomal enzyme, beta-N-acetylhexosaminidase A (ref. 1). A relatively high frequency of carriers (1/27) of a lethal, infantile form of the disease is found in the Ashkenazi Jewish population, but it is not yet evident whether this has resulted from a founder effect and random genetic drift or from a selective advantage of heterozygotes. We have identified a single-base mutation in a cloned fragment of the HEXA gene from an Ashkenazi Jewish patient. This change, the substitution of a C for G in the first nucleotide of intron 12 is expected to result in defective splicing of the messenger RNA. A test for the mutant allele based on amplification of DNA by the 'polymerase chain rection and cleavage of a DdeI restriction site generated by the mutation revealed that this case and two other cases of the Ashkenazi, infantile form of Tay-Sachs disease are heterozygous for two different mutations. The occurrence of multiple mutant alleles warrants further examination of the selective advantage hypothesis.

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Until adults develop a more pragmatic ideology in relation to children's rights then a true respect for children's autonomy will not be achieved. Consent will therefore remain an adult and legal prerogative.