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d-bifunctional protein (d-BP) deficiency is thought to lead to severe lipid metabolism disorders. To investigate the effect of naturally occurring missense mutations in the hydratase domain in d-BP, we constructed several d-BP hydratase variants and measured their activities. Missense mutations at sites whose conservation rates among 30 eukaryotes were < 70% did not affect hydratase activity. We predicted that missense mutations of highly conserved amino acids would markedly reduce activity. However, R562H and R562L, naturally occurring missense mutations of highly conserved amino acids, did not reduce activity. This result suggests that a missense mutation in a highly conserved amino acid does not always lead to severe lipid metabolism disorders. We also investigated the effect of G525V, which had been found in a mildly symptomatic patient with d-BP deficiency who was heterozygous for G525 and G658X. G525V markedly reduced hydratase activity. We had predicted that heterozygous G525V and G658X would lead to severely disordered lipid metabolism. However, the symptoms were inconsistent with this prediction. Characterizing mutations in the d-BP gene and the symptoms of d-BP deficiency may require pleiotropy, not only in vitro, studies.

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A flying erase head structure has been optimized to achieve sufficient erasability for Hi-Vision VTR systems with high coercive (> 1,500 Oe) metal particle magnetic tapes. Preferable erase head drive conditions have also been determined from erasability dependence on erase current amplitude and head core arrangements to the magnetic tape running directions with a 21.4m1s relative velocity. It was found that the most superior· erasability over -30dB is obtained with 45mA erase current at 20MHz erase frequency in the MIG head with Sendust films on both sides of the head gap edges, which is assured by 2-dimensional numerical analysis.lt has also been clarified that the erase head field transition width and the number of the erase head field reversals in the transition width are important factors for determining the erasability in the high frequency recording.

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