An adaptation is described which makes the common propipette readily acceptable for repetitive use. The application of pressure from an appropriate gas to permit rapid delivery of fluids and a method by which the propipette may be used comfortably in one hand make this tool amenable to routine use in a practical attempt to reduce the risks of contamination to both the operator and his cultures.
adenine dinucleotide transhydrogenase activity in cells cultured from rat hepatoma. Can. J. Biochem. SO, 447-456 (1972).Preparations from cells cultured from a minimal-deviation hepatoma in the rat exhibit pyridine nucleotMe transhydrogenase (NAD(P)H: NADV) oxidoreductase, EC 1.6.1.1) activity. The pH optimum, its release by digitonin, and its apparent lack of dependence on steroids for activity tentatively classifq. it as a transhydrogenase of the type first described for animal tissue. Enzyme preparations from digitonin-treated homogenates were very unstable. The time necessary for the loss of one-half the activity was 16-18 h when the enzyme was stored at 5 "C; this was reduced to 4 h when storage was in polycslrbonate tubes.The enzyme apparently transferred hydrogen directly and with equal ease from NADH to both the 3-acetylpyridine and thionicotinamide analogues of NAD. Half-saturation values for NAD and its acetylpyridine analogue were 0.99 x lo-' M and 3.55 x lo-* M, resgectively. The enzyme exhibited its maximum activity in phosphate buffer at pH 5.8. It was inhibited by 50-60% over the pH range 7.0-8.5 in Tris buffer. This could be reversed by dithiothreitol; reversal was complete between pH 8.0 and 8.5.Da LUCA, C., et G I O~I , R. P. Pyridine-adenine dinucleotide transhydrogenase activity in d s cultured from rat hepatoma. Can. J. Biochem. SO, 447-456 (1972).Nous avons d h l e l'activitk d'une pyridhe nuclbtide transhydrogtnase (NAD(P)H: NAD(B) oxydodductase, EC 1.6.1 .l) dans des pdparations de cellules cultivh I partir d9un hkpatome du type "minimddeviation" chez le rat. A cause de son pH optimum, de sa 1iGration par la digitonine et du fait que son activitk ne semble pas dkgendre des stkroides, nous suggirons de classifier cet enzyme comme une transhydroghase du type d'abord &rit pour les tissus anhaux.Les prtparations e-atiques provenant d9homo&nats trait& a la digitonine sont tds instables. L'enzyme perd la moitik de son activitk en 16-18 h quand il est gardi t i 5 "C; ce temps est rkduit I 4 h si I'enzyme est gardt dans des tubes Be polysarrbonate. I1 semble que l'enzyme transfhre diratement et avec une Cgale facilite I'hydroghe du NADH sup les deux analogues 3-adtylpyridine et thionicotinamide NAD. Les valeua de demi-saturation pour le NAD et son analogue dtylpyridine sont respectivement de 0.99 x lo-' M et 3.55 x lW4 M. L'activitk de renzyme est maximum dans un tampon phosphate ii pH 5.8. Dane le tampon Triq entre les pH 7.0 et 8.5, l'enzyme est inhibk de 50-60%. Cette inhibition p u t Stre renversk par le dithiothrkitol; le renversement est total entre les pH 8.0 et 8.5.
An adaptation is described which makes the common propipette readily acceptable for repetitive use. The application of pressure from an appropriate gas to permit rapid delivery of fluids and a method by which the propipette may be used comfortably in one hand make this tool amenable to routine use in a practical attempt to reduce the risks of contamination to both the operator and his cultures.
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