1. The distribution of iron in 59Fe-labelled pigeon (Columba L.) leg and breast muscle and liver were determined by gel filtration. While the insoluble Fe was between 14 and 25% of the total Fe from the tissues, the haem-Fe represented 79.1% (breast) to 45% (liver) of the total Fe and ferritin was between 5.5% (breast) and 26.5% (liver) of the total Fe.

2. The tissue haem-Fe concentration was found to be lower than that determined by gel filtration using the method of Schricker et al. (1982) for non-haem-Fe and obtaining haem-Fe by difference.

3. A simulated in vitro digestion procedure showed significantly (P < 0.01) reduced 59Fe solubility from 59Fe-labelled pigeon meat after cooking at 90° for 30 min.

4. 59Fe absorption from whole pigeon meat and soluble extract was significantly reduced by cooking when given to Fe-replete rats. Cooking liver, however, slightly improved 59Fe absorption in Fe-replete rats.

5.59Fe absorption from the separated pigeon-meat fractions (haemoproteins, ferritin and haemosiderin) was variable but considerably lower than that from whole meat.

6. The relative distribution of Fe compounds in meat, the processing conditions they are subjected to and the protein content and composition may all influence the absorption of meat-Fe to some degree.

1. Soya-bean proteins were used to replace 30 and 50% of the protein from 59Fe-labelled pigeon (Columbn L.) and chicken meat, and the solubility of the meat 59Fe in vitro and its absorption in vivo in rats in the presence and absence of soya-bean proteins were measured.

2. Replacement of part of the chicken meat by soya-bean proteins reduced 59Fe solubility from chicken meat at all stages during simulated in vitro digestion.

3. 59Fe absorption from 59Fe-labelled chicken meat when given to both Fe-replete and Fe-deficient rats was reduced in the presence of soya-bean proteins but was unaffected by the presence of casein or bovine serum albumin. 59Fe-absorption from pigeon meat in the presence of soya-bean proteins was not reduced to the same extent as that from chicken meat.

4. There was no significant effect of soya-bean proteins on 59Fe-labelled haemoglobin Fe absorption in vivo in Fe-replete rats.

5. Absorption of 59Fe from the isolated haemoproteins from chicken meat was unaffected by soya-bean proteins but 59Fe absorption from the main non-haem-Fe fractions was strongly inhibited, particularly from haemosiderin.

1. The availability of lysine in four meat meals (MMs), four meat and bone meals (MBMs) and two blood meals was determined using the slope-ratio assay with growing pigs, rats and chicks and with two chemical techniques.

2. The availability of lysine (proportion of total) in the eight MMs or MBMs ranged from 0.48 to 0.88 for pigs, from 0.49 to 0.88 for rats and from 0.68 to 0.88 for chicks. There was no apparent relation between the availability estimates for pigs, rats and chicks for the individual meals.

3. For the two blood meals, availability estimates were 1.03 and 1.13 for pigs, 0.81 and 0.80 for rats and 1.07 and 1.02 for chicks.

4. Values for the indirect and direct 1-fluoro-2, 4-dinitrobenzene-‘available’-lysineassays ranged from 0.77 to 0.88 and 0.78 to 0.93 respectively for the eight MMs and MBMs. There appeared to be no relation between these values and the pig estimates.

1. The availability of lysine for pigs, rats and chicks was determined using samples of meat and bone meal (MBM) subjected to different pressure and temperature treatments during dry-rendering processing. The relation between slope-ratio estimates and three chemical tests for estimating ‘available’ lysine was assessed.

2. The availability of lysine (proportion of total) for pigs was 0.97 in the control. Pressure (275 kPa gauge, 141°, for 30 min) in the early stage of rendering reduced availability to 0.74 and, in the late stage, to 0.46. Maintaining the final temperature at 125° for 4 h had little effect (0.84) whereas a higher temperature of 150° for 4 h reduced availability to 0.38.

3. Availability estimates for rats were lower than those of the pig, ranging from 0.88 in the control to 0.21 for the high-temperature treatment (150° for 4 h). The effects for temperature were similar to those for the pig, whereas the effect of pressure was equally detrimental in both the early and late stages (0.45 and 0.43 respectively).

4. For chicks, availability estimates were similar to those for the pig for the control (0.93) and the two temperature treatments (0.86 and 0.31 for the 125° and 150° treatments respectively). The chick was less susceptible to the effect of pressure applied to the MBM (0.78 and 0.63 for the early-and late-stage treatments respectively).

5. Values for the indirect-and direct-1-fluoro-2, 4-dinitrobenzene-(FDNB)-‘available’-lysine assays decreased from 0.86 and 0.74 to 0.57 and 0.54 for the control and 150° for 4 h treatments respectively, indicating that approximately half the reduced availability involved reactions with the ε-amino group of lysine. There was little relation between the FDNB values and lysine availability for the treatments involving changes in pressure.

6. There was little or no relation between dye-binding capacity of the meals, as assessed by the Acid Orange-12 dye-binding procedure (Hurrell et al. 1979), and lysine availability for the three species.

1. Riboflavin deficiency at two levels of severity was produced in weanling rats by feeding deficient diets for 6 weeks and using neck collars to prevent coprophagy. The severity of deficiency was monitored by growth, liver flavin levels and the activation coefficient of erythrocyte glutathione oxidoreductase (NAD(P)H) (EC 1. 6. 4. 2 ) Control groups, receiving the same diet with ample added riboflavin, were fed either ad lib., or were pair-fed with the deficient animals.

2. The hepatic flavoenzyme, methylenetetrahydrofolate reductase (NADPH) (EC 1.5.1.20), was very markedly affected by severe riboflavin deficiency and was significantly, but less markedly, affected by the intermediate level of deficiency. This reduction in activity was due primarily to the direct effect of the diminished supply of riboflavin, and occurred to only a small extent as a result of inanition, demonstrated by a moderate reduction in activity in the more severely food-restricted of the two pair-fed groups. Since the enzyme is assayed in the presence of its flavin cofactor, FAD, it clearly cannot be reactivated in vitro, as some other depleted flavoenzymes can. The discriminatory ability in distinguishing between severe and moderate riboflavin deficiency in vivo confers some potential advantages on this oxidoreductase as a possible index of riboflavin status.

3. The hepatic activity of another key folate-metabolizing enzyme, dihydrofolate reductase (EC 1.5.1.3), was not diminished by riboflavin deficiency in the present study.

4. The ratio, labelled 5-methyltetrahydrofolic acid: other labelled compounds derived from intraperitoneally injected pteroylglutamic acid in extracts of hepatic tissue was significantly reduced in the riboflavin-deficient groups, indicating the possibility of an effect of riboflavin deficiency on folate metabolism in vivo.