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The effects of purified fiber components and wheat bran on several indices of protein utilization were determined in growing rats. A control diet containing 10% casein was diluted with either cellulose (C), pectin (P), lignin (L), guar gum (G), or wheat bran (W) at fiber levels ranging from 3% to 20%. All fibers except C caused a decrease in net protein ratio (NPR) as compared to the control casein diet. This depression in NPR increased as the dietary fiber level increased. Apparent and true nitrogen digestibilities also decreased with all fibers at all levels. At the highest level of fiber (20%) the depression was greater for G and W and was least for C. NPR when divided by digestibility (analogous to biological value) decreased with P,L, W (all levels) and G (20% level) but not with C. When rats were fed fiber without protein, there was increased excretion of endogenous fecal nitrogen with all fibers at all levels. The results demonstrate that fiber(s) affected protein utilization as measured by NPR, digestibility and endogenous fecal nitrogen excretion and that the negative effect increased with the level of fiber consumed.

Forty-one strains of Kluyveromyces fragilis (Jörgensen) van der Walt 1909 varied 60-fold in ability to produce lactase (beta-galactosidase). The four best strains were UCD No. 55-31 (Northern Regional Research Center NRRL Y-1196), UCD No. C21(-), UCD No. 72-297(-), and UCD No. 55-61 (NRRL Y-1109). Biosynthesis of lactase during the growth of K. fragilis strain UCD No. 55-61 was followed on both lactose and sweet whey media. Maximum enzyme yield was obtained at the beginning of the stationary phase of growth. Bets lactase yields from K. fragilis UCD No. 55-61 were obtained with 15% lactose and an aeration rate of at least .2 mmol oxygen/liter per min. Supplementary growth factors were unneccessary for good lactase yeilds when yeast was grown on whey media. Best extraction of lactase from fresh yeast cells was obtained by toluene autolysis (2% vol/vol) at 37 C in .1 M potassium phosphate buffer, pH 7.0, containing .1 mM manganese chloride and .5 mM magnesium sulfate. The enzyme was concentrated and purified partially by acetone precipitation. At least 95% of the enzyme activity of the concentrated solution was retained after storage for 7 days at 22 C, for 3 wk at 4 C, and for 6 wk at -20 C.

Crude p-galatosidase was produced by lysis of cells of Streptococcus thermophilus grown on deproteinized whey. The enzyme was partially purified by ammonium sulfate precipitation and ion-exchange chromatography to yield a preparation free of protease activity. Highest activity was observed at pH 7.1, in the presence of potassium and manganese ions. Both monovalent and divalent cations were required for maximum activity but not for stability. The Km for o-nitrophenyl-p-galactopyranoside and lactose was 0.98 mM and 6.9 mM, respectively. Galactose was a competitive inhibitor with Ki of 60 mM. Gel-filtration indicated a molecular weight of 530,000. The enzyme seems well suited to hydrolysis of lactose in milk.

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